High School Living Earth Evidence for Evolution Lessons Name: School: Teacher

DO NOT EDIT--Changes must be made through “File info” CorrectionKey=CA-B

High School Living Earth Evidence for Evolution Lessons Name: School: Teacher:

The Unit should take approximately 4 days complete. Read each section and complete the tasks. CorrectionKey=CA-B DO NOT EDIT--Changes mustbemade through “File info” 188 plan your project. Worksheet tohelp the UnitProject Go onlinetodownload to be11 the MojaveDesertisestimated or makes itoneoftheoldestliving FIGURE 1: ganisms onEarth Unit 4Evidence forEvolution

700 yearsold This creosote ringin . . This and anyquestionsyouhaveaboutthem. questions. InyourEvidenceNotebook,recordwhatyoualreadyknowaboutthesetopics As youmovethroughtheunit,gatherevidencetohelpanswerfollowing provides shadetoitsshallowfeederroots. funnel rainwaterintothetaproot.Inwetterareas,bushhasamoreroundedshapethat to fitdifferentmicroclimates.Indrierareas,theplanthasaconeshapeinwhichstems and avastnetworkofshallowfeederroots.Creosotebushesexhibittwodifferentshapes increases. Italsohasarootsystemthatconsistsofbothanexceptionallylongtap for photosynthesisfromthemorehumidairandclosesthemasday’stemperature and fromgrazing.Itonlyopensitsstomatainthemorningtopullcarbondioxide are coatedinafoul-tastingresinthatprotectsitfromwaterlossthroughevaporation to cloneoutwardinringsratherthanrelysolelyonseedproduction.Theplant’sleaves has avarietyofadaptationstoitsdesertenvironment,includingreproductivetendency The creosotebushisthoughttobethemostdrought-tolerantplantinNorthAmerica.It UNIT PROJECT PREDICT evolution ofeyes? can leadtothedevelopment ofuniquefeatures,suchaseyes.Howcanyouexplainthe as thoseinhumans,letorganisms seeimages.Explorehowsmallchangesovertime Eyes arecomplexorgans.Simple eyesletorganismssense lightwhilecomplexeyes, such Investigating theEvolutionofEyes 1. 3. 2. DRIVING QUESTIONS How canwelearnaboutlifeonearlyEarth? species overtime? What arethemechanismsofnaturalselection,andhow do theyleadtochangesin How canwetracethelinesofdescentbetweenspecies?

How dospecieschangeovertimetoadjustvaryingconditions?

© Houghton Mifflin Harcourt Publishing Company TERM: evolution TERM: tectonicplate TERM: geologictimescale TERM: Definition Definition Definition Definition Similar Term Similar Term Similar Term Similar Term fossil understanding ofthescienceconcepts. Use thelessonsinthisunittocompletechartandexpandyour Language Development Phrase Phrase Phrase Phrase Example Example Example Example Unit 4Evidence forEvolution 189 CorrectionKey=CA-B DO NOT EDIT--Changes mustbemade through “File info” 190 LANGUAGE DEVELOPMENT TERM: heritable TERM: artificialselection TERM: adaptation TERM: natural selection Definition Definition Definition Definition Similar Term Similar Term Similar Term Similar Term Unit 4Evidence forEvolution Phrase Phrase Phrase Phrase Example Example Example Example

4.1 Geologic Time

Red Rock Canyon State Park is made up of hills with distinctive layers of rock.

CAN YOU EXPLAIN IT?

Red Rock Canyon State Park in Southern California is known for the dramatic, colorful bands that run through the cliffs. The stripes in the cliffs are different layers of rock that were exposed over time. Within these layers, scientists have discovered more than 100 species of extinct plants and animals that lived from about 12 to about 8 million years ago. Red Rock Canyon has produced one of the most diverse arrays of fossil organisms in Western North America.

PREDICT How do you think the rock layers and fossils found in Red Rock Canyon can provide evidence for Earth’s geologic history? What types of information can scientists learn from fossils? © Houghton Mifflin Harcourt Publishing Company • Image Credits: ©Gary C. Tognoni/Shutterstoc

Evidence Notebook As you explore this lesson, gather evidence to explain how the history of life on Earth is revealed through rock and fossil records.

Lesson 1 Geologic Time 191 DO NOT EDIT--Changes must be made through “File info” CorrectionKey=CA-B

EXPLORATION 1

Sedimentary Rock and Fossils

Rock is natural, solid, nonliving material that makes up Earth’s crust and much of its interior. Most rock is composed of combinations of one or more minerals. Properties of a particular type of rock—such as color, texture, and mineral composition—are a result of how the rock formed. Through the rock cycle, rocks undergo physical and chemical changes. Other natural cycles are related to the rock cycle. For example, in the water cycle, moving water erodes weathered rock fragments and deposits them in new places where sedimentary rock layers can then form. Water also causes chemical changes as it dissolves rocks such as limestone and marble.

Evidence Notebook How do you think the characteristics of rock can be used to determine how it formed and what Earth was like at the time and place where it formed?

The Formation of Sedimentary Rock

Running water, flowing ice, wind, and gravity move pieces of rock, called sediment, from one place to another over Earth’s surface. Particles of rock settle out of water and air and accumulate as sediment on Earth’s surface. Over time, sediments are buried and compressed. Water moving through pores between the grains of sediment deposits natural cement that glues the grains together. A sedimentary rock forms.

FIGURE 1: Grand Staircase Escalante National Monument, Utah

INFER Which layers of sedimentary rock at Grand Staircase Escalante National Monument do you think are the oldest? Use evidence to support your claim.

Explore Online Sedimentary layers are deposited on top of each other. Unless the layers have

been disturbed, the oldest rocks are at the bottom and the youngest are at © Houghton Mifflin Harcourt Publishing Company • Image Credits: ©sumikophoto/Fotolia Hands-On Lab the top. Sediments are also deposited in relatively flat layers. For example, Determining the Relative when a river floods, mud, sand, and gravel are deposited in horizontal layers. Age of Rock Strata Model core Over time these layers are compacted and cemented together into hard rock. sampling and how large-scale forces The top layer makes up the surface of Earth. However, uplift and erosion can change rock strata. expose the layers below the surface. For example, a river can carve into an uplifted sequence of layers and expose them in the canyon or valley walls.

192 Unit 4 Evidence for Evolution CorrectionKey=CA-B DO NOT EDIT--Changes mustbemade through “File info”

© Houghton Mifflin Harcourt Publishing Company of fossilization. or sediment.Bones,shells,plantfragments,andbacteriacanallbefossilized. A fossilisthetraceorremainsofanancientorganismthatpreservedinrock Fossil Formation must occurforanorganismor itstracestobecomefossilized. and burrowshavebeenwashed away.Specificconditionsmustexistandcertainprocesses Instead, thebodiesofmostorganismshavedecomposed,andtheirfootprints fossilized. Uncountable organismshaveexistedonEarthovertime, butveryfewhavebeen ANALYZE processes involvedinfossilformationtakeplaceonthescaleofmillionsyears. FIGURE 2: b. a. d. c. left in the mud. the in left are Footprints break downcarbon-richmoleculesintheanimal. soon afterdeath,scavengersmayfeedonthefleshormicrobes An organismdiesandbeginstodecay.Iftheisnotburied Erosion revealsthelayerofrockinwhichanimalwasburied. Fossilization oftheanimalremainsoccursovertime. remain andtheseremainsareburiedwithinalayerofsediment. With thesofttissuesgone,onlyhardpartslikebones,teeth,andshells

Bones, teeth,footprints,andothertracesoflifecanbefossilizedorpreserved.The Use Figure2toorderthestepsinvolvedinprocess containing the bones and footprints. and bones the containing strata of layers the exposes Erosion and dies. and Dinosaur collapses bones bones remain. away; rots Flesh

dinosaur bones. the contains bed This water, and moving ice. moving water, and running wind, by eroded and weathered be would bones the exposed, left If footprints. and bones the buries sediment rises; level Water

bones fossilize. bones the gradually bones; the over accumulates sediments of A sequence

Cycles Explore theWaterandRock rock cycle. that involvesthewatercycleand investigation toexplainaprocess Lesson 1 Geologic Time Hands-On Lab Explor Plan andconductan e Online 193 CorrectionKey=CA-B DO NOT EDIT--Changes mustbemade through “File info” 194 organisms. physical remainsofancient FIGURE 3: b a c

frozen soil occurring asphalt Mammoth preserved in Mammoth preservedin Beetle preservedinnaturally Ants preservedinamber Unit 4 Body fossilsare Evidence forEvolution erosion, allowingforfossilization. environment, suchasalagoon,canalsoprotecttheorganismfrombeingexposedby body ofwatercanprotecttheorganismfromdecomposition.Burialinalow-energy rapidly buryanorganismforfossilizationtooccur.Alackofdissolvedoxygenina scavengers anddecomposersupondeath.Thismeansthatnaturalprocessesmust Preservation ofsoftbodypartscanonlyoccuriftheorganismisprotectedfrom your answer. tissues) oforganismswithskeletons. organism withoutaninternalorexternalskeleton,thesoftbodyparts(suchas interactions. Thisisespeciallytruewhentalkingaboutasoft-bodiedorganism,an The chancesthatanorganismdiesandbecomesafossildependoncomplex Probability ofFossilization APPLY Cause andEffect

What makessofttissuedifferentfromhardtissues?Useevidencetosupport correct answers. also preserved. shells, bones,teeth,andcellulose.Inrarecases,softpartssuchasmusclesare altered. Bodyfossilsgenerallyconsistofthehardpartsorganisms,suchas Body fossilsareremainsofancientorganismsthathavenotbeendramatically Body Fossils organism atall,butaresignsofitsexistence. crystals, oraresimplyimprintscasts.Stillothersnotpiecesofthe relatively unchanged.Mostfossilsdiscoveredhavebeenreplacedbymineral Some fossilsaretheactualpartsoforganismsthathaveremained Fossils canbeclassifiedbasedonhowtheyformandwhatrepresent. more commonly discovered. or bones,brokenabraded bonesandshells,orsmallfragmentsofwoodare More commonly,bodyfossils consistofpartsorganisms.Individualteeth Complete andwell-preserved fossils,suchasthoseshowninFigure3,arerare. INFER d. c. b. a. was alive. Scientists canlearnabouthowtheorganismfunctioned whenit the groupoflivingthingsfossilwaspartof. By comparingthefossiltoalivingorganism,scientistscan determine Scientists canlearnaboutthedailyactivityoforganism. The fossilscantellscientistsaboutthesizeandshapeof the organism.

What evidencecanscientistscollectfrombodyfossils?Select all

© Houghton Mifflin Harcourt Publishing Company • Image Credits:(t) ©Layne Kennedy/Corbis Documentary/Getty Images (c) ©Colin Keates/Corbis Documentary/Getty Images (b) ©Andrei Tkachev/ITAR-TASS Photo Agency/Alamy CorrectionKey=CA-B DO NOT EDIT--Changes mustbemade through “File info”

© Houghton Mifflin Harcourt Publishing Company • Image Credits: (tl) ©Chris Craggs/Alamy (tr) ©Millard H. Sharp/Science Source (b) ©Sinclair Stammers/Science Source a Once ahollowmoldforms,fluidsmayflowthroughit,slowlyfillingitwithminerals,forming molds donotpreservetheorganismitself,importantsurfacefeaturescanbepreserved. Although dimensional impressionofanorganismmayform.Thisisknownasamold. If thebodyofanorganismdecaysordissolvesafterithasbeenburied,athree- Molds, Casts,andImprints inferred onlyfromtracksand othertracefossils. where theyformed.Theexistenceofsomeorganismscan be fossils, theycanalsoprovideinformationabouttheenvironment for whereandhowanorganismlived.Inaddition,likeother trace organisms. Fossilizedburrows,showninFigure5,areevidence fossilized feces—canprovideinformationaboutthediet ofancient fast theanimalwalkedorran.Coprolites—piecespellets of while thespacingbetweenfootprintscanbeusedtoinfer how depth ofdinosaurtrackscanbeusedtoestimatetheanimal’s size, trails, provideevidenceforhowanorganismmoved.The sizeand variety oftracefossils.Some,suchasdinosaurtracksandworm signs oftheactivityorbehavioranorganism.Thereareawide impressions oforganisms.Instead,trace fossilsarepreserved Unlike bodyfossils,tracefossilsarenotactualpieces,molds,or Trace Fossils the organicmaterialdecomposesandisremoved. and insectsaresqueezedorcompressedbetweenlayersofsediment.Overtimemost film. Thesetwo-dimensionalfossilsformwhensoftmaterialandorganismssuchasleaves Sometimes allthatremainsofanorganismisadarkimprintcoveredinthincarbon-rich FIGURE 4: cast . Castscanalsobemadeoffinesedimentsthathavefilledthemold. a

ammonite. A cast(right)fillsthemold(left)ofan Evidence Notebook type offossil?Give specificexamplesinyouranswer. vertebrate speciesinRedRockCanyon. Whatcouldthescientistlearnaboutthisspeciesfromeach What kindofinformationcantheynotdetermineusingthesetypesfossils? fossils. Withapartner,discusswhatevidencescientistscangatherfrommoldsandcasts. Collaborate Casts andimprintsprovide evidencefortheshapeandsizeofanorganism. Molds andcastsareimprintsofbodyparts,butdonotcontainactual A scientistexaminesthebodyfossil andtracefossilsleftbyanancient b

structures ofthisleaf. Compression haspreservedthedelicate or coral, butitisactually fossilized burrows. FIGURE 5: Chondrites lookslike plantroots Lesson 1 Geologic Time 195 CorrectionKey=CA-A DO NOT EDIT--Changes mustbemadethrough “File info” 196 Timescale Geologic The EXPLORATION 2 Unit 4Evidence forEvolution 6 5 4 3 2 1 principle toconnectlayersofrockthatareseparatedbylongdistances. to theprincipleoffaunal succession. Scientistssoonrecognizedthattheycouldusethis combinations aremostlyconsistentfromplacetoplace.Theseobservationsgaverise vertically fromlayertolayer.Second,thegroupingsoffossilsandorder observations. First,inasetofsedimentarylayers,thecombinationfossilschanges In theearly1800s,scientistsstudyinglayersofrockinEuropemadetwoveryimportant The Fossil Record geologic timescale,whichseparatesEarth’shistoryintodistinctdivisionsoftime. year history.Bydeterminingtherelativeandactualagesofrocks,scientistsassembled Rock formations,andthefossilswithinthem,holdkeytounlockingEarth’s4.6billion- and Australianlayersthatarethesameage. correlate layersindifferentpartsoftheworld.DrawlinesconnectingEuropean evidence andreasoningbehindthis? on onecontinentformedatthesametimeasalayeranother continent?Whatisthe ANALYZE EXPLAIN European stratum3isthesameageas Australian stratume. European stratum1isthesameageas Australian stratumc. Europe 6 5 4 3 2 1 6 5 4 3 2 1 6 5 4 3 2 1 your listofquestionswithapartner. are found,andhowthatinformationcouldhelpthemunderstandthehistoryofEarth.Discuss Collaborate

How doestheprincipleoffaunalsuccessionsupport claimthatarocklayer Scientists canusethespecificcombinationsoffossilsinrocklayersto European stratum3isthesameageas Australian stratume. European stratum1isthesameageas Australian stratumc. European stratum3isthesameageas Australian stratume. European stratum1isthesameageas Australian stratumc. Europe Europe 6 5 4 3 2 1 European stratum3isthesameageas Australian stratume. European stratum1isthesameageas Australian stratumc. Europe 6 5 4 3 2 1

European stratum3isthesameageas Australian stratume. European stratum1isthesameageas Australian stratumc. Make alistofquestionsscientistsmightaskabouttypesfossils,wherethey Europe European stratum3isthesameageas Australian stratume. European stratum1isthesameageas Australian stratumc. Europe d b a e c f d b a e c f Australia d b a e c f Australia d b a e c f d b a e c f Australia Australia Australia d b a e c f Australia

© Houghton Mifflin Harcourt Publishing Company during thePaleozoic. fossils. Otherimportantindexfossilsincludedifferentspeciesoftrilobites,whichlived thus changedquicklyovertime,andareveryeasytoidentifydistinguish fromsimilar Tropites isaparticularlygoodindexfossil.TheywerewidespreadoverEarth,evolvedand organism representedbythefossillivedinawidevarietyofsedimentaryenvironments. distinguish from similarfossils.Thefossilshouldbeabundantinrocklayers.Finally,the and identify to easy be must fossil been widespreadonEarth,notjustinonesmallarea.The thousands toafewmillionyears—andthenbecomeextinct.The organism must have organism musthavelivedoverarelativelyshortperiodofgeologictime—hundreds To beusefulasanindexfossil,afossilmustmeetfewimportantrequirements.The e. d. c. b. a. 230 and208millionyearsago. example, Tropites, aspeciesofammonite,existedduringtheMesozoic,sometimebetween species areknownasindexfossilsbecausetheycanbereliablyusedtodaterocklayers.For some fossilswereparticularlyusefulforinferringtherelativeageofarocklayer.These based onfaunalsuccession,theyalsonoticedthat As scientistswerecorrelatingandclassifyinglayers called Cenozoic,or“newlife.” top andyoungestlayers,withmammalfossils,were bones werecalledMesozoic,or“middlelife.”Andthe middle layerscontainingammonitesanddinosaur classified asPaleozoic,meaning“ancientlife.”The lowest andoldestlayers,richwithtrilobites,were layers intobroadgroupsbyage.Forexample,the began torecognizethattheycouldorganizerock Using theprincipleoffaunalsuccession,scientists Index Fossils around theworldtodetermine thegeologictimescale? complete geologictimescale. of organisms.ThereisnooneplaceonEarthwhereyoucan findrocksrepresentingthe intervals basedonevidencefoundinlayersofrockandthe appearanceandextinctions geologic timescaleofEarth’shistory.The dividesEarth’shistoryinto Scientists havecombinedinformationfromfossilevidence allovertheworldtobuilda Visualizing theGeologic Timescale INFER APPLY Organism livedonEarthforhundredsofmillionsyears.good|poor Organism livedinaconcentratedarea.good|poor Organism becameextinct.good|poor Fossil issimilartootherfossils.good|poor Fossil isabundantinrocklayers.good|poor

Identify whethereachinstancewouldmakeagoodorpoorindexfossil. How canscientistsusethefossil recordandfaunalsuccessionfromlocations

FIGURE 6: Tropites existedforonlyabout20millionyears. Lesson 1 Geologic Time 197 CorrectionKey=CA-A DO NOT EDIT--Changes mustbemade through “File info” 198 FIGURE 7: Unit 4Evidence forEvolution 66.0 Ma 252 Ma 541 Ma 4 538 Ma Scientists usethegeologictimescaletounderstandEarth’s longhistory. Paleocene Cambrian epoch period Triassic period of a12-hourclockface. model thePrecambriantimeandPaleozoic,Mesozoic,Cenozoicerasinterms divided intoperiods,whichmaybefurtherepochs. era, theMesozoicandCenozoicerafollowedPrecambriantime.Thethreeerasare Precambrian. Eonsaredividedintoeras, whicharesmallertimesegments.ThePaleozoic geologic timeareeons,andthefirstthreetogethersometimesreferredtoas organized likeacalendarintotimedivisionsofdifferentlengths.Thelargest Geologists haveinterpretedtherockandfossilrecordtoshowthatEarth’shistorycanbe MODEL 56.0 Ma 485 Ma determined this? Whatcanyoulearnabout thesefossilsfromthegeologic timescale? that existedbetweenabout 12 and8millionyearsago.Howcouldscientistshave Evidence Notebook Ordovician

period Scientists oftenexplaingeologictimeintermsofaclock.Usingthisanalogy, 201 Ma Precambrian time(4 538 Mato541Ma) Eocene epoch Paleogene period

444 Ma Silurian period Cenozoic era(66.0Matopresent) Mesozoic era(252Mato66.0Ma) Jurassic period Vertebrate fossilsfoundinRed RockCanyonarefromspecies 419 Ma (541 Mato252Ma) Paleozoic era 33.9 Ma Devonian period Oligocene

epoch 145 Ma

Pennsylvanian period 359 Ma

23.0 Ma Mississippian Carboniferous period period Cretaceous Miocene Paleozoic era Neogene period epoch period 323 Ma Pliocene epoch Pleistocene epoch Mesozoic era Quaternary period Holocene epoch 299 Ma Cenozoic era

Permian 541 Ma period 5.3 Ma 252 Ma 2.6 Ma 66.0 Ma 0.012 Ma 66.0 Ma 252 Ma present present

© Houghton Mifflin Harcourt Publishing Company • Image Credits: ©Robert Malone/Alamy based onthetypesoforganismsfoundinrocklayers. example, scientistscandetermineiftheareawasanaquaticoraterrestrialenvironment also usefossilstodeterminehowtheenvironmentofaregionhaschangedovertime.For The fossilrecordprovidesevidencefortheevolutionoflifeonEarth,butscientistscan History of Life on Earth EXPLORATION 3 evolved inbothlocations,nor couldithavecrossedthesaltwaterAtlanticOcean. found inpartsofSouthAmerica andAfrica.ScientistsdonotthinkMesosauruscouldhave The fossilsofMesosaurus,afreshwaterreptilethatlivedabout270millionsyearsago, are Evidence of Tectonic Plate Movement conditions oftheoceanandatmosphere. about environmentandclimate.Fossilsofshellscorals provideevidenceofthepast invertebrate animals,andplantsporespollen.These fossilscanprovideinformation past climates.Microfossilsarefossilsofmicroscopicbacteria, single-celledprotists, Scientists canevaluatefossilsaswellpatternsoferosion anddepositiontodetermine scientists tointerpretevidencefromfossils. and oftheshapesstemsleavestoclimate. Examiningmodernorganismshelps about extinctorganisms.Theystudyrelationshipsofbonetomuscle,teethdiet, these specieswillbecomeextinct.Scientistsusemodernorganismstomakeinferences significantly, somespeciesmaynotbeabletoadaptthenewenvironment.Eventually, Earth’s ecosystemsareinaconstantstateofchange.Whenanenvironmentchanges those ofmodernbigcats,suchasleopards? environment ofasaber-toothedcatbycomparingitsfeatureswith organisms lived. can alsoprovideinformationaboutenvironmentsinwhichancient useful forcorrelatingandestimatingtheagesofrocklayers,they that thesamewastrueforancientorganisms.Notonlyarefossils make themadaptedtoparticularenvironments.Wecanassume We knowthatorganismsalivetodayhavespecificfeatures Evidence Provided by theFossil Record ANALYZE more abouttheconditions ofEarthatthistime? the Collaborate

What couldyouconcludeaboutthebehaviorand Mesosaurus inbothSouthAmericaandAfrica. Whatquestionsmightscientistsasktolearn With apartner,discusspossibleexplanations forwhyscientistsfindfossilsof

scientists withevidenceabouthowitlived. from thePleistoceneepochcanprovide FIGURE 8: This fossil ofasaber-toothed cat Lesson 1 Geologic Time 199 CorrectionKey=CA-B DO NOT EDIT--Changes mustbemade through “File info” 200 FIGURE 9: Unit 4Evidence forEvolution AMERICA SOUTH Locations ofMesosaurusfossil discoveries AFRICA major animals groupspresentonEarthtoday evolved. million yearsago duringtheCambrianperiod. Withinabout40million years,almostall One ofthegreatestevolutionary changesinlifeformsEarth’shistorystartedabout 540 The CambrianExplosion one ofthemostimportanttransitions inthehistoryoflife. one steptowardmulticellularorganisms.Thetrend multicellularorganismswas originated aslongago2.1billionyears.Colonialcellular organismsarethoughttobe that colonialcells available allthetime.RecentstudiesoffossilsinGabon, Africa andChina,indicate As scientistscontinuetheirresearch,newevidenceforthe historyoflifeonEarthbecomes eukaryotes, andmulticellularorganisms. enough oxygentoallowfortheevolutionoforganismswithcellsorganelles,called oxygen production.Scientistshaveinferredthatthissecondoxygenationeventsupplied After agapofalmostbillionyears,photosyntheticorganismscausedanotherspikein organisms tookalongtimetorecover. the land,resultinginmassextinctionofunicellularorganisms.Theoxygen-producing and glaciersformed.Sea-icecoveredmostoralloftheocean As aresultofremovingsomuchcarbondioxidefromtheair,Earthcooleddramatically ago, theyhadproducedenoughoxygentocausetheGreatOxidationEvent. carbon dioxideandproducedoxygenduringphotosynthesis.Byabout2.3billionyears one ofthemostimportantinfluencesonearlyEarth’satmosphereandclimate.Theyused lacked anucleusorothermembrane-boundorganelles.Recallthatcyanobacteriawere much ofthetimeperiod.UntillatePrecambrian,allorganismsweresingle-celledand after Earth’sformation,temperatureswerequitehighwithaslowcoolingthroughout There islittledirectevidenceaboutclimateduringthePrecambrian.Itlikelythatsoon Unicellular andMulticellularLifeForms think hasthemostsupport. that supportsorrefuteseachtheory.Prepareapresentationdescribing whichtheoryyou including thetheoryofendosymbiosis.Researchatleasttwotheories andrecordevidence Language ArtsConnection been found fossils have Mesosaurus Areas inwhich —cells livingtogetherbutnotpartofthesameorganism, mayhave over time. movement causesthecontinentstochangeposition surface, thesetectonicplatesarealwaysmoving.This currents andthemotionofrockfrombeneathEarth’s of rockcalledtectonicplates.Duetoconvection over time.Earth’soutersurfaceismadeoflargepieces has helpedtoshowthatEarth’ssurfacemoved different continents.Evidencefromthefossilrecord Many othersfossilshavealsobeendiscoveredacross were connectedinonelandmass. suggest thattheorganismsexistedwhentheseregions geographical rangeofeachfossil.Patternslikethis puzzle pieces.Therearedistinctpatternsinthe Figure 9,youwouldfindthattheyfittogetherlike If youputtheselandmassestogether,asshownin

There areseveraltheoriesfocusedoneukaryoticevolution,

© Houghton Mifflin Harcourt Publishing Company • Image Credits: (l) ©O. Louis Mazzatenta/National Geographic/Getty Images (r) ©James L. Amos/Science Source plant andanimalpopulations. combination withpoisonoushydrogensulfidekilledoffthemajorityofperiod’s extinction eventschangedeverything.Evidencesuggeststhatanoxygencrashin sediment andpredation.AttheendofCambrianperiod,oneEarth’smajormass organisms weredevelopingnewecologicalinteractions,suchasburrowingintosoft record fromCambriansediments.Someofthesetracefossilsprovideevidencethat were especiallyabundant.Thefirstcomplextracefossilsarealsofoundinthefossil vertebrates wasagroupofjawlessfishes.Marineinvertebrates,suchasthetrilobites, At thestartofPaleozoicera,alllifewasfoundinocean.Amongearliest could scientistsdeterminewhethertheseorganismsarerelated? INFER FIGURE 10: stability overthelongterm,andchangeshortterm? This isanexampleofcoevolution. developed spinesandotherfeaturesthatallowedthem to avoidpredation. the evolutionoflargepredators.Thisaffected trilobites, which favored Paleozoicmarineinvertebrates.Ecologicaldiversity wasexpandedby climate, andhighsealevelsproducedshallowseasallover Earth.Theseconditions different. DuringtheOrdovician,marineecosystemsexpanded inauniform Following theCambrian–Ordovicianextinctionevent,life becamedramatically Coevolution intheFossil Record EXPLAIN a

Marrella splendens

Do youthinkthetwoorganismsinFigure10belongtosamegroup?How Stability andChange These fossils are from theCambrianperiod.

How dotheevolutionarydevelopmentsoftrilobites represent is anancientarthropod. b

Modocia typicalis isatypeoftrilobite. Lesson 1 Geologic Time 201 CorrectionKey=CA-B DO NOT EDIT--Changes mustbemade through “File info” 202 angiosperm, Glossopterisbrowniana. FIGURE 11: Unit 4Evidence forEvolution A fossil impression ofaMesozoic out, asdidmarinereptilesand dominantinvertebrates. reptiles. TheMesozoicended withanothermassextinction,duringwhichdinosaurs died they appeartonothaveevolved anddiversifiedthroughouttheMesozoiceraasmuch as their fossilsarerare.Primitive mammalsalsoevolvedduringthelateTriassicperiod, but The firsttruebirdsemerged from bird-likedinosaursduringtheJurassicperiod,though through theMesozoic,expandingtheirrangetoinclude marineenvironmentsandtheair. animals ontheplanet.Dinosaursandotherreptilescontinued toevolveanddiversify late Triassic,dinosaursandtheirreptilerelativeshadreplaced themastheprincipalland early Mesozoic,mammal-likereptileswerethedominant terrestrialvertebrates.Bythe began around250millionyearsagoandlasteduntil 66millionyearsago.Inthe The Mesozoiceraisknownastheageofdinosaurs,or,often, theageofreptiles.Thisera The AgeofDinosaurs deposits thatarestillbeingminedtoday. present atall,theorganicmatterinplantmaterialwasconvertedintorichcoal swamps. Whenthisvegetationwasburiedinaplacewhereoxygenlimitedornot Carboniferous period,about359millionyearsago,vegetationaccumulatedincoastal the land.Landplantscontinuedtobecomemorediverseandabundant.By began about419millionyearsago,forestsofclubmosses,horsetails,andfernscovered The firstlandplantsappearedduringtheOrdovicianperiod.ByDevonian,which The RiseofLandPlants to becomethedominantanimalsonplanet. extinction eventmarkedthetransitionintoMesozoicera,duringwhichdinosaursrose in thedeathof81%to96%marineorganisms,and70%landorganisms.Thismass history, approximately252millionyearsago.Itisthoughtthattheextinctionresulted The PaleozoiceraendedwiththemostcatastrophicmassextinctioneventinEarth’s INFER remains becamecoaldeposits. and didnotcyclebackintotheatmosphereasoxygen|carbondioxidewater—the cut offfromoxygen|carbondioxidewater.Asaresult,thestayedinplace | thousandsofyearsago.Plantsgrewinswampsandtheirremains,underwater,were The coaldepositscurrentlybeingusedasanenergyresourceformed

Complete thestatementbyselectingcorrectterms. to evolve.Withapartner,discusswhyyouthinkthesegroupsoforganismsevolvedtogether. of floweringplants.Anincreaseinthevarietyinsectscausedmoretypesplants Collaborate to determinewhichofthesehypothesesmaybemoreaccurate. angiosperms weresmallherb-likeplants.Researchcontinuestotry by scientiststoday.Theotherhypothesissuggeststhattheearliest hypothesis issupportedbyseverallinesofevidence,andfavored plants—trees similartomodernmagnoliasandlaurels.This One originsuggeststhattheearliestangiospermswerewoody studying theangiospermshavesuggestedtwopossibleorigins. 125 millionyearsagoduringtheCretaceousperiod.Scientists Angiosperms, alsoknownasfloweringplants,developedabout Insects wentthroughanevolutionaryexplosioninresponsetotheevolution

billions |millions

© Houghton Mifflin Harcourt Publishing Company • Image Credits: ©Spencer Sutton/Science Source share acommonancestor? between dinosaursandmodernbirds? feathers originallyhadanotherfunctionintheropods. with feathers,buttheydidnothavewings.Theywererunninganimals.Thismeansthat that feathersdidnotoriginateasanadaptationforflight.Thesetheropodswerecovered over 200millionyearsagoduringtheTriassicperiod.Thisimportantdiscoveryshowed In the1990s,scientistsdiscoveredtheropodfossilswithfeathers.Theyfirstappeared theropods wereancestorsofmodern-daybirds. two legs,suchasTyrannosaurusrex.Duetosharedfeatures,scientistshypothesizedthat a groupofdinosaursknownastheropods.Theropodswerethatwalkedon In the1970s,scientistsobservedthatArchaeopteryxsharedmanyuniquefeatureswith and acurved“killingclaw”oneachofitssecondtoes. long tail.Unlikemodernbirds,italsohadajawwithsharpteeth,threefingersclaws, dinosaur wasaboutthesizeofamodern-dayraven.Ithadbroad,roundedwingsand Archaeopteryx livedaround150millionyearsagointhelateJurassicperiod.Thisbird-like detailed andwell-preservedfossilshavebeenfoundsinceitwasfirstdiscoveredin1860. meaning itisanintermediatebetweendinosaursandmodernbirds.Onlytwelvevery shares featuresofbothbirdsanddinosaurs.Itisconsideredtobeatransitionalfossil, Archaeopteryx hasbeencalledboththefirstbirdanda“feathereddinosaur”becauseit

ANALYZE GATHER EVIDENCE

What additionalevidencewouldhelpsupporttheclaim that theseorganisms to ModernBirds Dinosaurs Connecting Ancient Structure andFunction

What patternsinanatomicalstructuresprovideevidence ofalink

Lesson 1 Geologic Time modern birds. the ancestorsof are thoughttobe of dinosaursthat an extinctgroup Theropods are FIGURE 12: 203 CorrectionKey=CA-B DO NOT EDIT--Changes mustbemade through “File info” 204 in theLaBrea tarpitsinCalifornia. FIGURE 14: FIGURE 13: Unit 4Evidence forEvolution A Columbianmammothfound A modernbisongrazing. ago, istheearliestknownhominin tomakestonetools. to 3millionyearsagoinAfrica. Homohabilis,whichlivedinAfrica2.4to1.5 millionyears placed intwogenera:Homo and Australopithecus.Australopithecusafarensislived4million Hominins—a generaltermthat groupshumansandourextinctancestors—arecommonly Modern-day humansevolved relativelyrecentlycomparedtootherspeciesontheplanet. The AgeofHumans populations ofmegafaunadwindleduntiltheyeventually becameextinct. this timeandhuntedtheseorganismsforfoodother resources.Overtime,the to warm,around10 Most oftheselargemammalsbecameextinctattheend oftheiceagewhenEarthbegan early Eoceneepoch,mostofthemajorgroupsmammalslivingtodayhadevolved. Cenozoic era,about4 of theMesozoicera,mammalsbecamedominantgrouponEarth.Duringearly The firstmammalsevolvedduringtheMesozoicera.Aftermassextinctionatend The AgeofMammals about theorganismsthatlivedingrasslandsduringCenozoicera? ANALYZE

How mightscientistsstudymodernanimals,suchasbison,tolearnmore 000 yearsago.Humansalsospreadtodifferentcontinents during 000 speciesofmammalsevolvedinabout10millionyears.Bythe grasses todatediscoveriesthistimeperiod. for bothhumansandlivestock.Scientistsoftenusethepollenfrom growing theirownfood,grassesbecameaprimarysourceoffood As humanstransitionedfromprimarilyhuntingandgatheringto also contributedheavilytothedevelopmentofhumanagriculture. and stomachswithmultiplecompartmentstodigestgrass.Grasses such ashigh-crownedteethtoimprovetheirabilityeatgrass, of grazinganimals.Theseanimalsevolvedtohaveadaptations as Earthcooled.Theincreaseingrassesgaverisetotheevolution the Mesozoicera.TheystartedtospreadduringCenozoicera case. Fossilevidencesuggeststhatgrassesfirstappearedduring Today, grassgrowsallovertheworld,butthatwasn’talways The RiseofGrasses California andtherestofNorthAmericaduringthistime. These fossilsprovideimportantevidenceabouttheclimate in pollen, andothermicrofossilshavealsobeenfoundatLa Brea. animals intothepits,alsobecomingtrapped.Plants,insects, and died.Sometimes,carnivoresscavengersfollowedthese California. Animalsenteredthepits,becametrappedintar, have beenpreservedintheLaBreatarpitsLosAngeles, ground sloths.Skeletonsoftheseorganisms,andmanyothers, megafauna includemammoths,saber-toothedcats,andgiant mammals ofaparticularregionorhabitat.Someexamples The Pleistoceneepochisnotableforitsmegafauna—large

© Houghton Mifflin Harcourt Publishing Company • Image Credits: (t) ©Eastcott Momatiuk/Photodisc/ Getty Images (b) ©Martin Shields/Alamy Images DO NOT EDIT--Changes must be made through “File info” CorrectionKey=CA-B

One of the most recent hominin relatives to modern FIGURE 15: The skull of Homo neanderthalensis (left) humans was Homo neanderthalensis, which lived compared with a skull of a human (right). from 430 000 to about 40 000 years ago in Europe and the Middle East. Some evidence suggests that Homo neanderthalensis coexisted with modern Homo sapiens. Fossil evidence reveals that Homo sapiens evolved between 200 000 and 100 000 years ago in what is now Ethiopia in Africa. However, many of their features were different than those of modern humans. Neanderthals had many distinct features, such as angled cheekbones and a wide nose that was adapted to humidifying the cold, dry air in their environment.

Collaborate What type of evidence could support the claim that Homo sapiens and Homo neanderthalensis coexisted? Discuss your answer with a partner.

Fossil evidence suggests that Homo sapiens began to leave Africa to inhabit other continents approximately 60 000 years ago. It’s unknown what exactly caused this migration, but one possible explanation could have been a change in climate that occurred during the final portion of the ice age. As humans spread and populated different continents, they began to influence both the evolution and extinction of organisms in other ecosystems. Some species were hunted to extinction, while humans transported other species from one continent to another, both unintentionally and intentionally.

Engineering

Designing Solutions for Endangered Species

Scientists think that we are currently living through another mass extinction event. Evidence suggests humans are part of the cause. Human activity has often been behind the extinction or endangering of many species. People, though, are taking steps to try to prevent the extinction of some species. California condors are a species of large bird dating from the Pleistocene epoch. Human activities, such as the use of the pesticide DDT and the construction of power lines, reduced the number of these birds to only 22 individuals by the 1980s. Organizations in California placed the remaining birds in captivity and started breeding programs. Using practices such as artificial incubation, these organizations hatched enough condors to release some birds into protected California habitats. Due to these efforts, there are now over 400 California condors.

EXPLAIN How might you use engineering, either by designing a device or process, to help reduce the impact of human activity on a local species? © Houghton Mifflin Harcourt Publishing Company • Image Credits: ©Pascal Goetgheluck/ Science Source

Evidence Notebook Fossils discovered in Red Rock Canyon have been dated to many different eras. What additional evidence could help scientists date these fossils?

Lesson 1 Geologic Time 205 DO NOT EDIT--Changes must be made through “File info” CorrectionKey=CA-A

TAKE IT FURTHER

Data Analysis

The Absolute Age of Rocks

Determining absolute time involves making measurements and calculations that are based on changes and rates of change in natural systems. However, the most accurate and precise method for measuring time relies on changes that happen to individual atoms. This method of measuring time is called radiometric dating.

Radiometric Dating FIGURE 16: Carbon-14 Decay Radiometric Dating

100 Percent of carbon-14 Percent of 1 half-life nitrogen-14

C remaining 50 14 2 half-lives

3 half-lives 4 half-lives

Percent of 25

12.5 6.25 0 0 5730 11 460 17 190 22 920 Time passed in years

Scientists can determine the age of some fossils through the process of radiometric dating. This technique uses calculations that are based on a radioisotope’s steady rate of decay. Isotopes are atoms of the same element that have different numbers of neutrons. For example, all carbon atoms have six protons, but the number of neutrons may vary. The most common carbon isotope has six neutrons in its nucleus. Because the atomic mass of an atom is equal to the sum of protons and neutrons in its nucleus, this isotope is known as carbon-12, or 12C. In the isotope carbon-14, or 14C, there are still six protons but eight neutrons, which add up to 14. Many elements have multiple isotopes, most of which are stable. However, some isotopes are unstable, or radioactive. This means that they give off radiation as they decay, or break down over time. Decay rates differ widely and are known for each isotope. Figure 17 lists a

few radioactive isotopes that are used in radiometric dating. © Houghton Mifflin Harcourt Publishing Company The decay of any radioisotope happens at a known, constant rate and is expressed as the isotope’s half-life. A half-life is the amount of time it takes for half of the original mass of the isotope to decay into the product, or daughter isotope. By measuring the amount of parent isotope remaining along with the amount of daughter isotope remaining, you can calculate a ratio.

206 Unit 4 Evidence for Evolution

bi_cnlese539273_465a 10-19-16 Leslie Kell CorrectionKey=CA-A DO NOT EDIT--Changes mustbemade through “File info”

© Houghton Mifflin Harcourt Publishing Company in afossilwillhavedecayedinto 11 3. The half-lifeof dies, itsintakeofcarbonstops,butthedecay The isotope 14 through eatingandbreathing,so 2. 1. meteorite samplesconsistentlyestimateEarth’sageatabout4.5billionyears. an unspoiledsampleforradiometricdating.Uranium-to-leadisotoperatiosinmany thought tohaveformedataboutthesametimeasEarth.Therefore,meteoritesprovide to Earth’ssurfacefromspace—donotgetrecycledorundergoerosion.Meteoritesare Unlike Earth’srocks,meteorites—whicharemostlypiecesofrockandironthathavefallen undergoes erosionandrockrecycling,rocksonEarthdonotremainintheiroriginalstate. Scientists have usedradiometricdating to determineEarth’s age. Because Earth constantly could beupto40millionyears. one percent.However,thismeansthatforasampleis4.4billionyearsold,theerror be about4.4billionyearsold.Therateoferrorforthistechniqueisverylow—lessthan dated usingradioisotopes.Theycontainedsmallmineralcrystalsthatwerecalculatedto of almostanyfossilorrocksample.TheoldestknownrockswerefoundinAustraliaand The predictabilityofradiometricdatinggivesscientistsareliabletooltocalculatetheage ANALYZE C remains. Isotope (parent) rubidium-87 uranium-238 FIGURE 17: which radioactiveisotopewouldyouuse?Explainyouranswer. If youareexaminingrocklayersthatsuspectedtobe about20millionyearsold, 17 If youmeasuredtheageofafossilusing If arockcontains75%ofthedecayproduct,howmanyhalf-liveshavepassed? 400 years,ortwohalf-lives,75%ofthe 000 yearsold,howmuchoftherockshouldbemade PLATE TECTONICS

INVESTIGATING Use thefigurestoanswerfollowingquestions. Isotopes usedinradiometric dating. 14 C iscommonlyusedtodaterecentremains.Organismsabsorbcarbon 14 C isroughly5700years.Thismeansthatafteryears,halfofthe Product (daughter) strontium-87 lead-206 14 14 N, itsdecayproduct.Theotherhalfremainsas C isconstantlybeingresupplied.Whenanorganism Half-life (years) 48.8 billion 4.5 billion OWN TIMESCALE 14 BUILD YOUR C willhavedecayed.Only25%oftheoriginal 14 C datinganddetermineditsagetobeabout 14

C continues.

Isotope (parent) potassium-40 carbon-14 14 COASTAL EROSION N? INVESTIGATING Product (daughter) argon-40 nitrogen-14 14 C. After 14 C of theseotherpaths. Go onlinetochooseone Lesson 1 Geologic Time Half-life (years) 1.3 billion 5730 207 DO NOT EDIT--Changes must be made through “File info” CorrectionKey=CA-B

EVALUATE

Lesson Self-Check

CAN YOU EXPLAIN IT?

FIGURE 18: The fossiliferous Dove Spring Formation is exposed in the hills of Red Rock Canyon State Park.

The geology of Red Rock Canyon reveals a fascinating look at a Cenozoic world that no longer exists. To biologists, however, the rocks of the Dove Spring Formation are particularly fascinating. These rocks are formed from sediments, lava flows, and ash that were deposited in an ancient valley. This valley no longer exists, but tectonic plate movement along the El Paso Fault elevated these rocks, exposing them to the elements. Thousands of individual fossils have been found in the rocks of the Dove Spring Formation. Most of the fossils found in the canyon come from species that lived between about 12 and 8 million years ago.

Evidence Notebook Refer to your notes in your Evidence Notebook and the information above to explain how Red Rock Canyon provides evidence for Earth’s geologic history. 1. Make a claim about how the rock layers and fossils exposed in the walls of Red Rock Canyon provide evidence for Earth’s geologic history. 2. What is the significance of the fossils preserved in the Dove Spring Formation to our

understanding of Earth’s history? © Houghton Mifflin Harcourt Publishing Company • Image Credits: ©Gary C. Tognoni/Shutterstock 3. How does rock and fossil evidence help us to gain an understanding of Earth’s history?

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Name Date CHECKPOINTS

Check Your Understanding 5. Which of the following would make the best index fossil? 1. Select the correct terms to complete the statement a. An insect that only existed in one small forest about trace fossils. for about 100 million years. Trace fossils are preserved signs of the b. An aquatic animal that existed all activity or behavior | mineralized remains | over the world for about 15 million years. c. A single-celled organism that lived in a soft parts of an organism rather than actual widespread region for about 25 million years. pieces, molds, or impressions of organisms. While d. A plant species that lived in a specific fossilized imprints | bones | footprints and tracks | geographic region for about 5 million years. muscles and tissues are not the only kind of trace 6. Select the correct terms to complete the statement fossil, they are the best known. about early life on Earth. 2. Which of the following statements about the When life first evolved on Earth, there was principle of faunal succession is true? Select all virtually no oxygen in the atmosphere. The correct answers. earliest prokaryotes were likely anaerobic | a. It relies on radiometric dating techniques. aerobic meaning they did not require oxygen b. It assumes that rock layers are to produce energy. Over time, photosynthetic deposited on top of one another. | chemosynthetic prokaryotes evolved, which c. It assumes that rock layers are deposited beneath one another. made energy from the sun. The chemical reactions d. It assumes that specific combinations involved in this process released carbon dioxide of organisms were living only at a certain | oxygen | nitrogen into the atmosphere. This time in Earth’s history. allowed for the evolution of eukaryotes. 3. Match the evidence to what scientists can learn from that evidence. 7. Which of the following statements are true about the Cambrian Explosion around the transition dinosaur tracks/ animal’s pace between the Precambrian and the Paleozoic era? worm trails Select all that apply. size and depth of diet of ancient a. Life-forms evolved from unicellular organisms dinosaur tracks organisms to more complex organisms. b. Photosynthesizing organisms first spacing between how an organism appeared in the fossil record. footprints moved c. Most major groups of animals first appeared coprolites size of an organism during this time period. d. The Cambrian Explosion occurred over a very long span of time. 4. Which of the following shows the correct progression of organisms on the planet?

Lesson 1 Geologic Time 209 DO NOT EDIT--Changes must be made through “File info” CorrectionKey=CA-B

EVALUATE

CHECKPOINTS (continued)

8. How does the presence of similar fossils on different continents support the idea of tectonic plate movement? Use evidence to support your claim.

9. How did the spread of early Homo sapiens from Africa to other continents likely influence populations of other organisms?

10. Why is the late Cambrian thought of as the period of the greatest evolutionary change in life forms in Earth’s history?

MAKE YOUR OWN STUDY GUIDE

In your Evidence Notebook, design a study guide that supports the main idea from this lesson: The fossil record provides much of the evidence to support evolution. Remember to include the following information in your study guide:

• Use examples that model main ideas. © Houghton Mifflin Harcourt Publishing Company • Record explanations for the phenomena you investigated. • Use evidence to support your explanations. Your support can include drawings, data, graphs, laboratory conclusions, and other evidence recorded throughout the lesson. Consider how scientists use patterns to analyze and draw conclusions about rock layers and fossils.

210 Unit 4 Evidence for Evolution DO NOT EDIT--Changes must be made through “File info” CorrectionKey=CA-A

4.2 Lines of Evidence for Evolution

A long-tailed pangolin perches on a tree.

CAN YOU EXPLAIN IT?

Long-tailed pangolins are truly unique animals. Each of these tree-dwelling creatures is covered in large, scale-like armor that makes it look like a walking pine cone. Although it may be mistaken for a reptile at first glance, the long-tailed pangolin also shares characteristics with mammals. It has fur on its face, abdomen, and the underside of its legs. As the name implies, it has an extremely long tail that is used to grip and move about trees where it feeds on ants, termites, and other insects. A long nose and sharp claws help the pangolin dig out ants from their nests. The fascinating combination of characteristics make this animal one of the most unusual creatures on Earth.

PREDICT Pangolins share many characteristics with different types of animals. How do scientists determine the evolutionary relationships between different organisms? © Houghton Mifflin Harcourt Publishing Company • Image Credits: ©Fabian von Poser /imageBROKER/Alamy

Evidence Notebook As you explore this lesson, gather evidence used to support common ancestry and evolutionary relationships among different species.

Lesson 2 Lines of Evidence for Evolution 211 CorrectionKey=CA-B DO NOT EDIT--Changes mustbemade through “File info” 212 Developmental and Anatomical Evidence EXPLORATION 1 FIGURE 1: a

Larval barnacle Unit 4 Barnacles andcopepodslooksimilarduringtheirlarvalstage. Evidence forEvolution determine evolutionaryrelationshipsbetweendifferentspecies? similarities amonginvertebrates. other hand,usetheirswimminglegstomovearoundand capturefood. animals. Theymustrelyontheirfoodtocomethem.Microscopic copepods,onthe and behaviors.Barnaclesbecomestationaryanimals,attaching tosolidstructuresorlarger striking similaritiesaslarvaeeventhoughadultsthey take onverydifferentbodyforms example, barnaclesandcopepodsarebothtypesofcrustaceans. Theseanimalsshow Invertebrates haveaninitiallarvalstageinwhichmanyspecies lookquitesimilar.For Developmental Similarities species. AnexampleofbiologicalevidenceisshowninFigure1. their ancestors.Biologicalevidenceisusedtoevaluateandidentifyrelationshipsbetween Evolution istheprocessofbiologicalchangebywhichdescendantscometodifferfrom evidence, suchasthefossilrecord,hasalsohelpedtoexplainevolutionofspecies. Scientists havegatheredgeologicalevidencetopiecetogetherEarth’shistory.Geologic PREDICT EXPLAIN that manyinvertebrateshave common|differentancestors. there areoftenobviousdifferences |similaritiesinbodyform.Thisevidence suggests The larval|adultstageofinvertebratesisavery earlystageofdevelopmentinwhich b

Adult barnacles How canbiologicalevidencesuchaswhatisshowninFigure1beusedto Select thecorrecttermstocompletestatementabout developmental c

Larval copepod d

Adult copepod(SEM)

© Houghton Mifflin Harcourt Publishing Company • Image Credits: (l) ©D.P. Wilson/FLPA/Science Source (cl) ©Patrick W. Grace/Science Source (cr) ©Sinclair Stammers/Science Source (r) ©Steve Gschmeissner/Science Source CorrectionKey=CA-A DO NOT EDIT--Changes mustbemadethrough “File info”

© Houghton Mifflin Harcourt Publishing Company common ancestry? common ancestry. ear andthroatstructures.Biologistsuseshareddevelopmentalpatternsasevidenceof pharyngeal archesbecomegills.Inmammals,however,developinto eventually differentiateinbothstructureandfunction.Forexample,adultfish pharyngeal arches,justasfishdo.Structuresthatappearverysimilarinearlydevelopment features inallfourvertebrateembryosshownFigure2.Humanhaveatailand features asembryos—atail,limbbuds,andpharyngealarches.Notethesecommon All vertebrates,animalswithaninternalsegmentedbackbone,havethreebasicbody bones intheir forelimbs. independently. Forexample, allfour-limbedvertebrates,ortetrapods,sharehomologous would beunlikelyformanyspecies tohavesuchsimilaranatomyifeachspeciesevolved appearance acrossdifferent species offersstrongevidenceforcommondescent.It organisms thatsharestructural similaritiesbutmayhaveverydifferentfunctions.Their evolutionary relationships.Homologous structuresarefeaturesfoundindifferent There aredifferenttypesofanatomicalstructuresthatscientists studytodetermine Homologous Structures ancestor. have multiplestructuresincommon,itsuggeststhatthe speciesshareacommon involves thestudyofsimilarstructuresfoundamongdifferent species.Ifdifferentspecies support theconceptofcommonancestryandevolutionary theory.Anatomicalevidence In additiontoevaluatingdevelopmentalsimilarities,scientists useanatomicalevidenceto Anatomical Evidence ANALYZE FIGURE 2:

All vertebrates gothrough astageofdevelopmentwithcommonfeatures. How doesthepatternofsimilaritiesinvertebrateembryoshelpsupport ihrpiebird reptile fish pharyngeal arches tail pharyngeal arches tail human Lesson 2

Lines ofEvidence forEvolution 213 CorrectionKey=CA-B DO NOT EDIT--Changes mustbemade through “File info” 214 FIGURE 3: a a

Parrot wings Human hands Unit 4Evidence forEvolution Bird wingsanddragonfly wingsare examplesofanalogousstructures. each x-rayimage. membranes. Thesimilarfunctionofwingsinbirdsandflyinginsectsevolvedseparately. For example,birdwingshavebones.Incontrast,insectdonotbones,only wings developdifferentlyinbirdsandinsects,theyaremadeofdifferenttissues. wings havesimilarshapesandstructuresbecausetheyarebothusedforflight.However, Compare thewingsofparrottothosedragonflyinFigure3.Bothbirdandinsect structures arethatperformasimilarfunctionbutnotinorigin. use ourarmsandhandsthesamewaythatabatusesitswing.Incontrast, body plan,buthavedivergedintodistinctstructuresbecauseoftheiruse.Wedonot Homologous structuressuchasthebatwingandhumanhandarebasedonsame Analogous Structures ANNOTATE terms ofsimilarities?Howdothesimilaritiessupportcommonancestry? Evidence Notebook

Use coloredpencilsormarkerstocolorinthehomologousstructures b

Bat wings What patternsdoyounoticeinthestructuresabove b

Dragonfly wings c

Dog feet analogous

© Houghton Mifflin Harcourt Publishing Company • Image Credits: (tl) ©domin_domin/iStockPhoto (tc) ©Nick Veasey/Getty Images (tr) ©Irina Alyakina/Fotolia (bl) ©Peter Schoen/Moment/Getty Images (br) ©asfloro/Fotolia CorrectionKey=CA-B DO NOT EDIT--Changes mustbemade through “File info”

© Houghton Mifflin Harcourt Publishing Company evolved fromlandmammals? analogous structures.Termscanbeusedmorethanonce. as thefemurinhumans. the humpbackwhale,asshowninFigure4.Thepelvisnormallysitsnearlegbones,such clues toanorganism’sevolutionarypast.Considerthetracesofpelvicbonespresentin gradually havelostallormostoftheirfunctionovertime.Vestigialstructuresprovide know isthatthesevestigialstructuresareremnantsofonce-important explaining whyflightlessbirdshavewingsorhumansatailbone.Whatwenow about structuresthatseemtoservenofunctionatall?Earlyscientistshadtrouble Common bodystructurescanbecomemoresimilarorlessovertime.Butwhat Anatomical comparisonscanshedlightonevolutionaryrelationshipsbetweenspecies. Vestigial Structures ANALYZE EXPLAIN FIGURE 4: Homologous structuresmaybeusedfor evolved from evidence ofcommonancestry. structures maylook Evidence Notebook the pangolinshares acommonancestorwithother animals? between pangolinsandotheranimals? Whatadditionalevidencewouldhelpsupporttheclaimthat

Many whalespecieshavevestigialpelvicandlegbones. Use thecorrecttermstocompletestatementabouthomologousand How doestheevidenceshowninillustrationsupport theideathatwhales developmentalpatternsandbasicstructure.Analogous What similaritiesinanatomicalstructures provideevidenceofalink different structures.Homologousstructuresare similar inappearancebut

functionsbut have Lesson 2 Linesof EvidenceforEvolution 215 CorrectionKey=CA-B DO NOT EDIT--Changes mustbemade through “File info” 216 Evidence Genetic and Molecular EXPLORATION 2 FIGURE 5: Unit 4 We share manyofourgeneswithotherorganisms. Evidence forEvolution common ancestor? molecular level. will havebuiltupineachlineage, andthemoredifferenttwospecieswillbeat passed sincetwospecieshave divergedfromacommonancestor,themoremutations rate ofmutationsisthe“ticking” thatpowersamolecularclock.Themoretimehas Molecular clocksaremodels thatusemutationratestomeasureevolutionarytime.The Molecular Clocks Molecular Similarities understanding ofevolution. molecular informationtheyhaveincommon.Thisevidencehelpstostrengthenour of livingthings,scientistscandeterminerelationshipsamongorganismsbasedonthe evolutionary relationshipsamongspecies.ByexaminingDNAandotherbiomolecules organisms. Scientistsnowusemolecularandgeneticdatatosupportclaimsabout advanced, sotoohasourabilitytoanalyzeevolutionaryrelationshipsbetweendifferent common ancestryamongorganisms.Astechnologyandanalyticaltechniqueshave Developmental andanatomicalsimilaritiesprovidescientistswithvisualevidenceof EXPLAIN

How dopatternsinDNAsupporttheclaimthatlivingthings sharea

fruit fly? about 47percentidenticaltothatofa surprise: DidyouknowthatyourDNAis However, thismightcomeasabitof considering micearemammals,too. mouse. Thatmaynotbetoosurprising about 88percentidenticaltothatofa think. For example,yourgenomeis species aresmallerthanyoumight sequences inthegenomesofvarious be. Thedifferencesinthenucleotide are, the moresimilartheirDNAwill general, themorerelatedtwospecies genetic codesofdifferentspecies.In technology, scientistscancomparethe our genome.ThroughDNAsequencing four basicnucleotidesthatmakeup their geneticcode.Weallhavethesame All livingthingsonEarthshareDNAas

© Houghton Mifflin Harcourt Publishing Company nuclear DNAasevidenceforevolution? many generationsinasinglespecies. is passeddownunshuffledfrommothertooffspringtracemutationsbackthrough mitochondria inaspermcellarelostafterfertilization.ScientistsusethefactthatmtDNA closely relatedspecies.AndmtDNAisalwaysinheritedfromthemotherbecause times fasterthanthatofnuclearDNA,whichmakesmtDNAagoodmolecularclockfor own DNA,calledmitochondrialDNA(mtDNA).ThemutationrateofmtDNAisaboutten Recall thatmitochondriaaretheenergyfactoriesofcells.Theseorganelleshavetheir Mitochondrial DNA relationships. mutation asthey arepassedon,sotheyprovide anotherwaytodetermine evolutionary longer functionbutarestillcarried withfunctionalDNA.Theycanalsochangethrough Pseudogenes alsoprovideevidence ofevolution.Pseudogenesaregenesthatno Pseudogenes in therRNAofdifferentlineagesarerelativelyclearandcan becompared. rate relativetomostDNA.Overlongperiodsofgeologic time,mutationsthatdobuildup molecule likerRNAsinceithasconservativeregionsthat accumulatemutationsatalow studying therelationshipsamongspeciesoverlongertime scales,itisbesttousea Ribosomes, whichmanufactureproteinsincells,contain ribosomalRNA(rRNA).When Ribosomal RNA ANALYZE

b. d. a. c.

descent. mtDNA isonlyinheritedfromthemother,makingiteasier totracelinesof evidence ononesex. mtDNA isonlypassedontofemales,soscientistsareablebetterfocustheir possible commonancestry. mtDNA isinheritedfrombothparents,providingawiderviewofinheritanceand over time. mtDNA mutatesataslowerrate,sotherearefewerchangestoanorganism’sDNA

Why mightanevolutionarybiologistbenefitfromstudyingmtDNAratherthan grandparents parents child subject torecombination. generation, soitisnot the motherofeach passed downonlyfrom Mitochondrial DNAis nuclear DNA mitochondrial DNA back throughgenerations. totrace it moredifficult from bothparents, making Nuclear DNAisinherited Lesson 2

Lines ofEvidence forEvolution to nuclearDNA. mitochondrial DNAcompared FIGURE 6: Inheritance of 217 CorrectionKey=CA-B DO NOT EDIT--Changes mustbemade through “File info” among species. conclusions aboutsimilarities results ofyouranalysistodraw and eukaryotes.Thenusethe protein commontobacteria Analyze similaritiesina Relationships Predicting Evolutionary Hands-On Activity 218 Explore Online Unit 4

Evidence forEvolution

least relatedtohumans? animals inthistableare millions ofyearsago(mya)eachanimalfirstappearedinthefossilrecord. and thehemoglobinofseveralotheranimals.Thetablealsoindicateshowmany The tableshowsthenumberofaminoaciddifferencesbetweenhumanhemoglobin differences increaseswiththeevolutionarytimebetweeneachgroupofspecies. can alsocomefromfossilevidence.Forexample,thenumberofaminoacid ancestor, theycanfindthemutationrateformoleculearestudying.Alink real time.Ifscientistsknowwhenthespeciesbegantodivergefromacommon To estimatemutationrates,scientistsmustfindlinksbetweenmoleculardataand Linking MolecularandFossil Data information fromthetableinyouranswer. the fossilrecordasevidenceforcommonancestryacross species?Usespecific EXPLAIN ANALYZE

b. d. a. c.

frog mouse shark horse and ConsistencyinNatural Systems Scientific Knowledge Assumes anOrder between wormsandvertebrates. proteins inthecellsofvertebrateeye.Thisshowsasharedancestry sensitive cellsinabrain-likestructureofanancientwormcloselyresemble most likelyhaveacommonancestor.Forexample,theproteinsoflight- different species.Cellsfromspeciesthathavethesameproteins Digital databasesofproteinsequencescanidentifysimilarin organisms. Auniquesetofproteinsisfoundinspecifictypescells. Comparing proteinscanalsorevealsimilaritiesamongcelltypesacross Protein Sequences

How doesthedataintablesupportuseofmolecular dataand Which two evolutionary relationships. types ofmolecularevidencethatscientistsusetosupport Collaborate

os 16 Mouse Horse Animal Bird Frog Shark With apartner,maketabletocomparethedifferent Compared withHumans Amino AcidDifferences

18 35 62 79 Appearance intheFossil Record (mya) 270 350 450 70 70

© Houghton Mifflin Harcourt Publishing Company for theincrediblediversityofbodytypesseentoday. animal. Scientiststhinkthatrandommutationsinthesekindsofgenesovertimeaccount or mutation,arisesinthesegenes,drasticchangescanoccurthebodyplanof of thegut,developmentawinginsteadleg,andsoforth.Ifrandomchange, tail. Fromtherethegenesdefinelocationandnumberofeyeslimbs, instructing embryoniccellswhereinthebodytheywillbelocated—head,midsection,or in thedevelopmentofanorganism’scharacteristicbodyplan.Theprocessbeginsby early stage,certaintypesofgenes,calledHoxhelptoguidetheprocessthatresults or birds,whythendoesabird’sbodyplanlooksodifferentfromourown?Fromvery body parts.IfwehavemuchofourDNAincommonwithotherorganisms,suchasmice As ananimaldevelops,itsgenesguidetheformationoforgansandarrangement Body PlanExpression duplication, thedevelopingorganismmayshowslightly differenttraits. along achromosome.Mutationsinthesegenesaretypically duplications,andwitheach caused theoriginalHoxgenetobecopiedrepeatedly,formingaseriesofsimilar genes fruit fliesandotherinsects.Thedifferencesuggeststhat over time,mutationshave plan areactuallyjustdifferentversionsoftheHoxgenethatdirectsbodyin have. Forexample,theHoxgenesthatdirectorganizationofvertebratebody Vertebrates havemultiplesetsofthesameHoxgenesthatinsectsandotherarthropods fruit fliesshareacommonancestor? humans andinfruitflies?Howdoyourobservationssupporttheclaimthat INFER FIGURE 7:

Evidence Notebook order todetermine theevolutionaryrelationshipbetween thepangolinandotheranimals? What patternsdoyouseeinthesimilaritiesanddifferencesbetween Differences infruitflyandhumanbodyplansarisefrom variationsinHoxgenes. HOXD HOXA HOXC HOXB What typesofcellularormolecular evidencemightascientiststudyin

Lesson 2 Hox genesin Lines ofEvidence forEvolution 219 CorrectionKey=CA-B DO NOT EDIT--Changes mustbemade through “File info” 220 The Tree of Life EXPLORATION 3 Unit 4 Evidence forEvolution your answer. turtles andtortoises,butnotbyorganismssuchasmammals? Usethediagramtoexplain these traits,orderived characters, aresharedbywhichspecies. some speciesbutarenotpresentinothers.Cladogramsbuiltbydeterminingwhichof out evolutionaryrelationshipsamongagroupofspeciesarethosethatsharedby some traitsfromitsancestorsthathavenotchanged.Thecanbeusedtofigure in somespeciesofacladebutstaythesameotherspecies.Eachhas group ofspeciesthatsharesacommonancestor.Throughevolution,certaintraitschange that showstheevolutionaryrelationshipsbetweengroupsoforganisms.Acladeisa A cladogramisadiagrambasedonpatternsofsharedtraits,orinheritedcharacteristics, Interpreting aCladogram A phylogenetic treevisuallyrepresentstherelationshipsamongspecies. Phylogenetics isthestudyofevolutionaryhistoryandrelationshipsorganisms. Scientists canusemultiplelinesofevidencetobuildevolutionaryhistoriesorganisms. ANALYZE FIGURE 8: tetrapoda clade. shared bytheentire recent commonancestor This noderepresentsthemost the intersectionoftwobranches. In acladogram, anodeis Node Tetrapoda amphibians clade

This cladogram showsthe relationships amongtetrapods, orfour-limbed animals. In thiscladogram,whatderivedcharacterissharedbyorganisms suchas Amniota mammals clade turtles/tortoises Reptilia clade with digits four limbs

lizards/snakes Diapsida by amnioticfluid embryo protected clade behind theeyes skull opening crocodiles/alligators side oftheskull openings inthe Archosauria not havethisderivedcharacter. amniota clade. Amphibians do shared byallorganismsinthe amniotic fluidisaderivedcharacter mark. An embryoprotectedby character representedbythehash a hashmarksharethederived after Organisms thatbranchoff Derived character clade the eyeandinjaw skull openingsinfrontof birds beaks toothless feathers and

© Houghton Mifflin Harcourt Publishing Company smallest arekingdom,phylum,class,order,family,genus,species. smaller levelswithfewerorganismsineachlevel.Theafterdomainfromlargestto organisms arecalleddomains.Eachhigherlevelwithinthehierarchyisbrokendowninto into groupsbasedonsimilarities.Inthissystem,thathavethelargestnumberof Scientists useaclassificationhierarchy,calledtaxonomicclassification,toplaceorganisms Taxonomic Classification descendants representaclade. nodes betweenspeciesindicatesahigherdegreeofrelatedness.Anancestorandallits points, orpointsofevolutiontwomorespeciesfromoneancestralspecies.Fewer are related.Thepointwherebranchesmeetiscalledanodeandrepresentsspeciation branches splitthroughoutthephylogenetictreegivesinformationabouthowspecies can rangefromasinglespeciestoanentireorder.Thelinesarethebranches.How The tipsofthebranchesonaphylogenetictreeindicategroupbeingstudiedand Bacteria andArchaea. genetically differentgroups of prokaryotes,splittingMoneraintotwoseparatekingdoms: 1959. Thiskingdomincludesmoldsandmushrooms.In1977, rRNAresearchrevealedtwo more aboutthenutritionofdifferentorganisms,afifthkingdom, Fungi,wasrecognizedin celled organismsthatlackmembrane-boundnucleiororganelles. Asscientistslearned called Monerawasestablished.Thiskingdomcontained prokaryotes, whicharesingle- kingdom wasmeanttocontainallsingle-celledorganisms. In1938,afourthkingdom plants andanimals.AthirdkingdomcalledProtistawasproposed inthe1860s.This domains didnotexistandtherewereonlytwokingdoms—Plantae andAnimalia,or develops andnewdiscoveriesaremade.Intheoriginalsystem developedinthe1700s, As withallbranchesofscience,ideasabouttaxonomychange asnewtechnology current kingdoms.Howwillscientistslikelyaddressthisnewdiscovery? PREDICT FIGURE 9:

b. d. a. c.

number ofspecies. Scientists willclassifythenewspeciesintokingdomthathasfewest propose anewkingdom. Scientists willeithermakeminorchangestothecriteriaforoneexistingkingdomor into theexistingsystem. Scientists willmodifyallofthelevelstaxonomysotheycanfitnewspecies Scientists willproposeanewkingdomonlyafterdiscoveringmorespecies. 1753 Two kingdoms animalia considered aworkinprogress? Collaborate

Suppose scientistsdiscoveranewspeciesthatdoesnotfitintoanyofthe The numberofkingdomsusedtoclassify organisms haschangedovertime. plantae

With apartner,discussthefollowing question:Whyistheclassificationoflife 1866 Three kingdoms animalia plantae protista 1938 Four kingdoms animalia plantae monera protista 1959 Five kingdoms animalia fungi Lesson 2 plantae monera protista

Lines ofEvidence forEvolution 1977 Sixkingdoms animalia fungi bacteria plantae protista archaea 221 CorrectionKey=CA-B DO NOT EDIT--Changes mustbemade through “File info” 222 Unit 4 Evidence forEvolution relationships impactedtaxonomyovertime? life model. Archaea, andEukarya.Thisisthesystemthatcurrentlyusedknownastreeof which isabovethekingdomlevel.Inthissystem,therearethreedomains:Bacteria, and theworkofotherscientists,Woeseestablisheddomaincategoryclassification, revealed thattheorganismswere,infact,verydifferentfrombacteria.Basedonhiswork as bacteria. However, evidence related to biochemical characteristics and DNA sequencing under conditionsofextremeheat,acid,andsalt.Theseorganismswereinitiallyclassified that liveinextremeenvironments.Previously,scientistsdidnotknowlifecouldexist exist. Hisproposalforthenewkingdomswasbasedondiscoveriesoforganisms Archaebacteria andEubacteriain1977,thedomaincategoryofclassificationdidnotyet When CarlWoeseproposedsplittingkingdomMoneraintothekingdomsof Classification Today ANALYZE FIGURE 10: permission ofNational Academy ofSciences, U.S.A. No. 15, 8392-8396. Copyright©2000byNational Academy ofSciences, U.S.A. Adapted andreproducedby Credit: Adapted from"Interpretingtheuniversalphylogenetictree"byCarlR. Woese from PNAS, Vol. 97, the number of differences inrRNAsequencesamongthesespecies. the numberofdifferences each ofthesixrecognizedkingdoms. The distancesbetweenbranchesareproportionalto Scientists constructedthisevolutionarytreebycomparingrRNAsequencesfromspeciesin Evidence Notebook you overcomethis challenge? might encounterifyouweretomake aphylogenetictreethatincludesthepangolin?Howwould

Kingdom: Bacteria How havetechnologicaladvancesandourknowledgeof evolutionary The tree oflifemodeldividesorganisms intothree domains. Domain: Bacteria Considering itsuniquecharacteristics, whatchallengedoyouthink Kingdom: Archaea Domain: Archaea

Kingdom: Protista Domain: Eukarya Kingdom: Plantae Kingdom: Fungi Kingdom: Animalia

TAKE IT FURTHER

Guided Research

Tracing the Evolution of Modern Humans

Evidence indicates that physical and behavioral FIGURE 11: A partially-crushed fossil Homo sapiens skull traits shared by all humans originated from apelike is prepped for analysis. ancestors. We evolved into modern humans over a period of approximately six million years. Developmental, anatomical, molecular, and genetic similarities support the idea that modern humans are closely related to apes. In fact, both humans and apes belong to the same classification group, primates. We share a common ancestor with the larger apes of Africa—chimpanzees and gorillas. It is thought that this common ancestor lived between 8 and 6 million years ago. Fossil evidence of intermediate forms of humans shows the progression of our body form over millions of years. The common ancestor of humans and apes was a primate that lived in the African grasslands, never moving far from trees. Then around 3 million years ago, these primates branched out and gave rise to an early group known as Australopithecus. Although they had many apelike features, this group of primates Language Arts Connection Using credible walked on two legs and used tools. Further branching print or online resources, conduct research over time led to the evolution of more human-like about new developments in our knowledge of human features and behaviors, such as a larger brain and the evolution. Use the following questions as a starting point for use of fire. the development of a research-based paper and informative Fossil evidence also indicates that humans first presentation. With your teacher’s approval, you may choose to evolved in Africa, with most of human evolution explore your own research questions. occurring there from 6 to 2 million years ago. • When and where was the first fossil of Australopithecus Eventually, humans migrated to Asia and then discovered? Europe, making their way to the Americas between • When and where was the first fossil of the modern 20 000 to 30 000 years ago. So, modern humans human (Homo sapiens) discovered? became widespread throughout the world only relatively recently. • How have scientists’ ideas of human evolution changed over time? With the advancement of technology and analytical • Have there been any recent discoveries that have led techniques, scientists continue to learn more about to changes in these ideas? human evolution and how we, as a species, have • Does molecular evidence support fossil evidence? changed over time. New discoveries of fossils and If so, how? improvements in dating techniques have helped us © Houghton Mifflin Harcourt Publishing Company • Image Credits: ©Marc Steinmetz/VISUM für GEO/ Redux gain a better understanding of when and how humans evolved. Future discoveries will undoubtedly deepen our knowledge of human evolution.

EVOLUTIONARY WHALE PREDICTING EVOLUTIONARY Go online to choose one BIOLOGIST EVOLUTION RELATIONSHIPS of these other paths.

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EVALUATE

Lesson Self-Check

CAN YOU EXPLAIN IT?

FIGURE 12: The long-tailed pangolin is a unique creature.

Long-tailed pangolins are animals with unique characteristics. They are covered in large, scale-like armor similar to reptiles. However, pangolins also have characteristics common to mammals, such as hair, mammary glands, and a jaw used to chew food. The pangolin has fur on part of its body and a long tail that is used to grip and move about trees where it feeds on insects such as ants. This interesting combination of features prompts ongoing questions about how pangolins are related to other organisms. Scientists had thought these animals might be related to anteaters, sloths, and armadillos. New evidence suggests pangolins may actually be more closely related to hyenas, bears, and wolves.

Evidence Notebook Refer to your notes in your Evidence Notebook to explain how scientists can use evidence to determine the evolutionary relationships between different organisms. 1. Make a claim about the evolutionary relationship between the long-tailed pangolin and other organisms. 2. How would you organize your evidence to support your claim? What evidence would

be most useful to support your claim? © Houghton Mifflin Harcourt Publishing Company • Image Credits: ©Fabian von Poser/imageBROKER/ Alamy 3. Why is the classification of organisms considered a work in progress? Use the pangolin as an example in your explanation.

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Name Date CHECKPOINTS

Check Your Understanding 5. The similarity in homologous structures between different species is evidence that they 1. By examining the fin of a primitive fish, scientists a. share a common ancestor. have found similarities in bone structure to that of b. are members of the same genus. modern day reptiles, birds, and mammals. What c. use the similar structures in the same way. type of evidence does this describe? d. evolved from each other. a. vestigial structures b. embryonic structures 6. Birds and snakes share a common ancestor from c. analogous structures over 250 million years ago, but now they show many physical differences. These differences are d. homologous structures most directly the result of e. molecular structures a. coevolution between species. 2. The Astyanax mexicanus is a species of tetra fish b. molecular clocks ticking at different that lives in bodies of water deep inside caves. rates. Even though they cannot see, these fish still c. the long-term accumulation of mutations. have small, non-working eyes. Their eyes are d. differences in the alleles of the examples of ancestor. a. vestigial structures. b. embryonic structures. FIGURE 13: Approximate Percentage of Shared DNA c. analogous structures. with Humans d. homologous structures. Organism Zebrafish Chicken Roundworm Chimpanzee e. molecular structures. Shared 70 60 21 98 3. How can a comparison of proteins help scientists DNA (%) identify a common ancestor between two species? a. It can reveal similar patterns in DNA 7. According to the table, humans share the most sequences. DNA with which of the following animals? b. It can help scientists identify a. zebrafish similarities among cell types. b. chicken c. It can confirm the presence of similar c. roundworm homologous structures. d. chimpanzee d. It can show similarities and differences in embryonic or larval development.

4. Select the correct terms to complete the statement. As embryos, all vertebrates share certain features such as pharyngeal arches | lungs. This provides

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EVALUATE

CHECKPOINTS (continued)

8. How are genes and proteins similar to homologous structures when determining evolutionary relationships among species?

9. The hummingbird is more closely related to a lizard than it is to a dragonfly. Explain why two species that look similar are not necessarily that closely related.

10. You have discovered the fossil remains of three organisms. One is mammalian, one is reptilian, and the third has both mammalian and reptilian characteristics. What techniques could you apply to determine possible relationships among these organisms?

MAKE YOUR OWN STUDY GUIDE

In your Evidence Notebook, design a study guide that supports the main idea from this lesson: Multiple lines of evidence support common ancestry and evolution. Remember to include the following information in your study guide: • Use examples that model main ideas. • Record explanations for the phenomena you investigated. © Houghton Mifflin Harcourt Publishing Company • Use evidence to support your explanations. Your support can include drawings, data, graphs, laboratory conclusions, and other evidence recorded throughout the lesson. Consider how patterns among the traits of different species are identified using developmental, anatomical, and molecular techniques.

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4.3 Theory of Natural Selection

An Anna’s hummingbird, native to Southern California, uses its long bill to feed from a flower.

CAN YOU EXPLAIN IT?

Within its narrow, needle-like bill is a hummingbird’s even longer tongue. Both of these specialized structures help the Anna’s hummingbird reach the nectar found within the trumpet–shaped flowers it feeds from. Both hummingbirds and flowers benefit when a hummingbird stops by a flower to feed, making theirs a mutualistic relationship. The hummingbird gets nutrient-rich nectar and the flower gets pollinated as the hummingbird moves from one flower to another of the same species.

PREDICT How do you think the hummingbird evolved traits, such as bill shape, that make certain flower species ideal food sources? And how did these flower species evolve the traits necessary to attract hummingbirds? © Houghton Mifflin Harcourt Publishing Company • Image Credits: ©Glenn Bartley/All Canada Photos/Alamy

Evidence Notebook As you explore the lesson, gather evidence for how natural selection results in species that are adapted to their environment.

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EXPLORATION 1

Hands-On Lab Modeling Natural Selection: Owls and Field Mice

We know from molecular, anatomical, and fossil evidence that species have FIGURE 1: Predator and Prey changed over time. This change is called evolution. But how does evolution actually occur in nature? In this lab, you will model one mechanism of evolution called natural selection. You will represent the predator, an owl in search of field mice. Your group will “consume” all the field mice that you can easily see until only 25 percent of the population remains. These surviving field mice will then reproduce. As with the hummingbird, the mice will pass on an important trait for survival to their offspring. You will continue the process for several generations of mice, with some being consumed and others surviving to pass on the traits that made them successful. a Barn owls are predators. MAKE A CLAIM How does a population change as a result of natural selection?

MATERIALS • construction paper, five colors b Mice are prey for barn owls. • piece of fabric

CARRY OUT THE INVESTIGATION 1. On the tabletop, spread out the fabric habitat given to you. 2. Count out 20 pieces of each of the five different colors for a total of 100 pieces. This will be your initial population of field mice. 3. One person should spread the pieces out randomly over the entire fabric habitat, making sure that none of the pieces covers the others. The remaining members of the group should not watch this process. 4. The remaining members of the group are now owls. They should pick up 75 pieces (field mice) as they see them, one by one, until a total of 25 field mice remain in the habitat. Be sure to count carefully. 5. Carefully shake off the habitat to remove the surviving mice (a total of 25). 6. Group the survivors by color, and record the numbers in your data table. 7. Next assume that each survivor has three offspring. Place three additional pieces of the

same color with each survivor. Record the number of each color in the table. Note that © Houghton Mifflin Harcourt Publishing Company • Image Credits: (t) ©selectimages/Fotolia (b) ©CreativeNature_nl/iStock/Getty Images there should again be 100 total pieces. 8. Mix up the new set of pieces. Have a different person spread them over the habitat. 9. Repeat the entire process (Steps 3 to 8) two more times, making a total of three generations of field mice that are preyed upon.

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© Houghton Mifflin Harcourt Publishing Company 3. 2. 1. ANALYZE COLLECT DATA Data Table1:EffectofPredationonFieldMicePopulationsOverTime Number atstart Number afterthirdreproduction Number afterthirdpredation Number aftersecondreproduction Number aftersecondpredation Number afterfirstreproduction Number afterfirstpredation Explain youranswer. Which traitsappeartobemostbeneficialforsurvivalinthis environment? What patternscanyouidentifyinthegrapheddata? Graph yourdatainthespaceprovided. Color 1 20 Color 2 20

Color 3 20 Color 4 20 Lesson 3

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4. Explain why the number of some mouse varieties increased over time while others decreased.

5. How do you think the data would have changed if the experiment were continued until a total of five generations of field mice were preyed upon?

6. What do you think would happen if you changed the environmental conditions and then ran the experiment again?

Mice can reproduce rapidly. In fact, their population could increase FIGURE 2: Female mice can have 5–10 litters per year. Over the span of a year, a single exponentially if given enough resources and few predators. mouse may produce 25–60 offspring. However, the greater the population, the more individuals must compete for resources, such as food, water, and mates. In addition, mice must escape predators to survive long enough to pass on their traits to their offspring. Any traits that help them survive and pass on their genes are considered beneficial in this environment. Natural selection is a mechanism by which individuals that have inherited beneficial adaptations show differential reproductive success. If the environment were to change, the traits that are beneficial could also change. If the grass in a field were to change colors due to a change in weather, different traits would be “selected for.” This does not mean that nature actually “chooses” traits. It simply means that some traits are passed down more often than others, because organisms with those traits are better able to survive and reproduce than others in their population that lack those traits. © Houghton Mifflin Harcourt Publishing Company • Image Credits: ©Steve Downer/ardea/Mary Evans Picture Library Ltd/age fotostock Evidence Notebook Apply the concepts from this activity to the hummingbird example. 1. Identify traits that help the hummingbird survive in its habitat. 2. What kinds of resources might hummingbirds compete for? 3. What types of traits would give a hummingbird an advantage over other members of its own species?

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© Houghton Mifflin Harcourt Publishing Company • Image Credits: (tl) ©Pictorial Press Ltd/Alamy (tr) ©SPL/Science Source (bl) ©Universal Images Group Editorial/Photo12/Getty Images (br) ©John Carnemolla/Shutterstock Early Ideas About Evolution theory ofevolutionbynaturalselection. of evolutionhadbeendiscussedformorethan100yearsbeforeDarwinproposedhis Charles Darwinisthescientistmostpeopleconnectwithevolution.However,concept Selection Natural of Theory the Developing EXPLORATION 2 we haveawidebodyofevidencethatsupportsDarwin’stheorynaturalselection. evidence thathasbeenrepeatedlyconfirmedthroughexperimentorobservation.Today, isaproposedexplanationbasedon develop atheoryforhowevolutionoccurs.A well adaptedforspecificenvironments.Darwinbuiltupontheworkofthesescientiststo Early scientistsobservedrelationshipsamongorganisms,andhowtheyseemedtobe FIGURE 3: that theorieschangeasnewevidence isdiscovered. Collaborate Ideas aboutevolutionhavedevelopedovertime. Discuss withapartnerhowtheinformation inthetimelinesupportsidea similarities. based upontheir and minerals plants, animals, organization for a newsystemof Linnaeus proposed Naturae Carolus 1735 Systema evolution. and thepossibilityof biological variation, organisms, sourcesof relationships among important ideasabout de Buffon,discussed Louis Leclerc,Comte Naturelle Georges- 1749 Histoire

enough foodforeveryone. challenge theworld’sabilitytosupply the increasinghumanpopulationwould Population ThomasMalthusarguedthat 1798 AnEssayonthePrincipleof 1794-1796 as competition. evolve throughmechanismssuch considered howorganismscould grandfather, ErasmusDarwin, Lesson 3 periods oftime. environmental changeoverlong evolution asoccurringdueto Jean-Baptiste Lamarckpresented 1809 PhilosophieZoologique

Zoonomia Darwin's Theory of NaturalSelection on Earthandareongoing. occurred ataconstantrate geological changeshave gradual andcatastrophic This theorystatesthatboth theory ofuniformitarianism. Charles Lyellproposedthe 1830 PrinciplesofGeology 231 CorrectionKey=CA-B DO NOT EDIT--Changes mustbemade through “File info” 232 that seemedtomatchtheirenvironment. elephantopus) hadvariationsintheirtraits FIGURE 5: b a

and shortlegs. long necks. tortoises allowsthemtostretchtheir Domed tortoiseshaveashortneck The highshelledgeofsaddle-backed Unit 4 Galápagos tortoises(Geochelone Evidence forEvolution Geology, whichhereadduringhistravels. Darwin collectedscientifictools,aswellbooks,oneofwhichwasLyell’s Darwin, arecentgraduatefromtheUniversityofCambridge.Topreparefortrip, collect specimensandstudynaturalhistory.AninvitationwasextendedtoCharles of SouthAmericaandthePacificislands.Theshipcaptainsawitasanopportunityto In 1831,theshipHMSBeaglesetsailfromEnglandonafive-yearjourneytomapcoast Darwin’s Voyage km FIGURE 4: mi 0 0 PACIFIC OCEAN 2,000 Darwin’s journeyontheHMSBeagle. 2,000 Galápagos Islands Valparaíso Callao Lima about variationoftraits. animals’ environmentsanddiets. similar species.Someofthesetraitsseemedwellsuitedto the on themainland.Hewasstruckbyvariationoftraits among island lookeddifferentfromthoseonnearbyislandsand those still studiedtoday.Darwinnotedthatthespeciesfound on one would makesomeofhismostwellknownobservationsthat are Islands, locatedoffthecoastofEcuador.Duringthisstop, Darwin Near theendofhisjourney,BeaglearrivedatGalápagos environments changed. also notedgeologicalphenomenathatmadehimwonderhow Islands andthosefoundonthecoastofSouthAmerica.Darwin differences betweenfossilsfoundonalaterstopintheFalkland approach lethimmakecomparativestudies,suchasnotingthe Darwin keptadiary,recordingeachnewobservation.This collect specimensofplants,animals,androcks.Asheworked, following year,theyoungnaturalistexploredrainforestto He wascuriousabouthowtheshellsendedupthere.During noticed abandofseashellsoncliffhighabovetheshoreline. The firststopoccurredattheCapeVerdeIslands,whereDarwin PREDICT with short|tall plants. The saddle-backed|domedtortoisewouldliveinanarea live inanenvironmentwith short|tallplantssuchasgrasses. The saddle-backed|domed tortoisewouldmostlikely ATLANTIC (Salvador) OCEAN OCEAN Azores Bahia

Falkland Islands Select thecorrecttermstocompletestatement Plymouth Janeiro Rio de

Cape Verde Islands Town Cape W INDIAN OCEAN Mauritius N S E Sydney Principles of Hobart PACIFIC OCEAN

© Houghton Mifflin Harcourt Publishing Company • Image Credits: (t) ©Gail Tanski/Alamy (b) ©John Warburton-Lee Photography/Alamy DO NOT EDIT--Changes must be made through “File info” CorrectionKey=CA-B

Among all of Darwin’s observations, the most cited are those of the Galápagos finches. These small birds, sometimes known as “Darwin’s finches,” are closely related, but have significant differences. These observations led Darwin to infer that species must somehow be able to adapt to their surroundings. An adaptation is a feature that lets an organism survive and reproduce in its environment. It was this analysis that eventually helped shape Darwin’s theory about how organisms change over time.

FIGURE 6: Different populations of Galápagos finches have traits that vary.

a Large cactus finch N GALÁPAGOS ISLANDS Isla Marchena (Geospiza conirostris) (Bindoe) W E PACIFIC Species in the genus Isla San Salvador Geospiza have thick beaks OCEAN C S a (Santiago, James) and can feed on large, hard n a Isla Fernandina l seeds that require strength I Isla San (Narborough) s a for crushing. b Cristóbal e l (Chatham) a Isla Isabela b Small tree finch (Albemarle) Isla Santa Cruz (Camarhynchus parvulus) (Indefatigable) Species in the genus Isla Santa María Camarhynchus have biting km 0 30 60 (Floreana, Charles) Isla Española (Hood) strength at the tips of their beaks, which is useful for mi 0 30 60 tearing vegetation.

EXPLAIN How do these finches’ adaptations help them survive and reproduce in their environment? What type of beak would you expect to see on a finch that eats insects? Explain your answer.

Since Darwin’s time, the evolution of populations on islands has been studied in many living organisms, such as fruit flies and honeycreepers, a type of bird on the Hawaiian Islands. Many of the same patterns have emerged. Island species appear closely related to mainland species, but they have adaptations matched to the conditions on the islands where they live. Adaptations are often very different in related species on islands that may be very close to each other, but have different habitats. Darwin was the first scientist to establish the relationship between island and mainland species. Today this is an important principle of biogeography, which is the study of the distribution of organisms around the world.

APPLY A species of finch on the mainland has a long, thin beak. It lives in swamps and its main food is insects. A closely related species of finch lives on an island near the mainland. This island has many trees that produce small, hard seeds. What kind of adaptation most

© Houghton Mifflin Harcourt Publishing Company • Image Credits: (t) ©Michelle Gilders/Alamy (b) ©Arco Images GmbH/Alamy likely became common in the island population, in response to its different environment? a. an even longer and thinner beak b. a medium-sized, thick beak c. a very large, thick beak d. a beak with a sharp tip

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Evidence forEvolution Select allcorrectanswers. research wasthe workoffarmersandbreeders. found greatinsightinhishome countryofEngland.OneimportantinfluenceonDarwin’s knowledge ofhowevolution occurs.Althoughhehadtraveledtheworld,Darwinalso After hisvoyage,Darwinspent morethan20yearsbuildingonhisresearchand to thisconcept,evolutionarychangesoccurslowlyover time, ratherthanallatonce. organisms. Theseobservationsledtotheconceptofevolutionary gradualism.According later extendedtheideasofanoldEarthandslow,gradual changetotheevolutionof that dailygeologicprocessescanadduptogreatchange overalongperiod.Darwin what hesawintheAndes.Darwin’sobservationsonhisvoyage supportedLyell’stheory above sealevel,theresultofaprocesscalledgeologicuplift.Thisexperienceexplained the effectsonsurroundingland.Thelandthathadbeenunderwaterwasmoved Andes Mountains.Darwinlaterexperiencedanearthquakeduringhisvoyageandnoted During hisvoyage,Darwinalsofoundfossilshellsofmarineorganismshighupinthe occur, Earthmustbemucholderthanpreviouslythought. some relationshiptofossilforms.Thesefossilssuggestedthatinorderforsuchchanges that thesefossilslookedlikethelivingspeciessuggestedmodernanimalsmighthave area, hefoundfossilsofhugeanimals,includingGlyptodon, agiantarmadillo.Thefact first introductiontothisstrange,armoredanimal.Whileonafossil-huntingtripinthe Blanca inArgentina.Whilethere,huntersbroughtbackanarmadillo.ThiswasDarwin’s Several yearsbeforeDarwinlandedintheGalápagos,BeagleanchorednearBahía being foundontopofmodern-daymountainranges?Select allcorrectanswers. ANALYZE EXPLAIN Illustrations notdrawn toscale. FIGURE 7: odon isnotpresentonEarthtoday. odon lookedexactlylikemoderndayarmadillos. odon hassimilarfeaturestothemodernarmadillo. odon hasaveryhardshell,whichisnotpresentinanymodernspecies. b. b. d. a. a. c.

geologic uplift geologic Glypt Glypt Glypt Glypt plate-tectonic forces plate-tectonic

Darwin foundfossils ofGlyptodon,whichresembles themodernarmadillo. Which typesofnaturalprocessescouldaccountforfossils ofmarineorganisms Which ofthesestatementsaresupportedbythe armadillo

d. c.

erosion sedimentation Glyptodon Glyptodon fossil?

© Houghton Mifflin Harcourt Publishing Company greatly alteredfromtheirwildformsthroughtheprocessofartificialselection. animals forthousandsofyears.Virtuallyallthefruitsandvegetablesweeathavebeen Humans havebeenusingartificialselectiontoselectfordesirabletraitsinplantsand that showthosetraits. selective agent.Humansdeterminewhichtraitsarefavorableandthenbreedindividuals process, humansmakeuseofthegeneticvariationinplantsandanimalsbyactingas of changingaspeciesbybreedingitforcertaintraitsiscalledartificialselection.Inthis Rather, theywerecontrollingwhichcowswouldbeusedtobreedoffspring.Theprocess The farmersandbreederswerenotcausingonecowtobemoreproductivethananother. certain traits,breederscouldproduceagreatamountofdiversitywithinananimalgroup. productive traitswerethenpassedontothefollowinggenerations.Throughselectionof would onlybreedthosecowsthatwerelargerandproducedmoremilk.These produced alotofmilk.OtherswouldbesmallerandproducefarlessThefarmer Farmers explainedtohimthat,forexample,somecowsgrewbigandstrong In England,Darwinobservedalotofvariationindomesticatedplantsandanimals. Artificial Selection has theability to bepasseddownfromone generationtothenext. their offspring.Forartificialselection tooccur,thetraitmustbeheritable.A heritable trait traits. Whenselectedandallowed tobreed,theseindividualswouldpasstheirtraitson to intervention, certainindividuals couldbeselectedtoproduceoffspringwithdesirable Although Darwinhadnoknowledge ofgenetics,heobservedthat,withhuman APPLY domesticated dogsisthegray wolf. FIGURE 8: to producemoreeffectiverescuedogs. thickest |thinnestfur,andbreedsonlythosedogsovermanygenerations a snowymountain.Thebreederchoosesthe A dogbreederwantstoproduceabreedofthatcanrescuepeoplefrom

Select thecorrecttermstocompletestatementaboutartificialselection. Domesticated dogsevolvedthrough artificialselection.Thecommonancestorfor (common ancestor) gray wolf gray largest |smallestpuppieswiththe Lesson 3

Theory of NaturalSelection 235 L. Kell 10-10-16 bi_cnlese539273_528a.ai CorrectionKey=CA-B DO NOT EDIT--Changes mustbemade through “File info” 236 Unit 4 Evidence forEvolution trait ispassedonornot. nature, however,theenvironmentgeneratesselectivepressurethatdeterminesifa not desirableor“useful.”Duringartificialselection,humansactastheselectiveagent.In advantageous tobreeders.However,breedersalsomightselectagainstfeaturesthatare selection, individualswithdesiredtraitsarebredovergenerations,butonlyifthe Darwin relatedwhathelearnedaboutbreedingtohisideasonadaptation.Inartificial group. Doyouthinkthatthenumberwillplateauatsome point?Explain. revolutions onthewheelperdayformiceinGeneration 10 oftheexperimental generations ofmicethatwereallowedtobreedrandomly. running wereselectedtobreedthenextgeneration.Thecontrolgrouprepresents increased wheel-runningbehavior.Themicethatwereabletodothemostwheel over severalgenerations.Inthisexperiment,micewereartificiallyselectedfor Scientists usedmicetostudywhetherexerciseabilitycanimproveinanimals

PREDICT ANALYZE Evidence Notebook color. Howmight thisadaptationbecomemorecommon overtime? Exercise Ability FIGURE 9: Patterns 1998 by Springer Science and Bus Media B V. Adapted and reproduced by permission of of permission by reproduced and BV. Adapted Media Bus and Science Springer by 1998 Genetics Behavior from al. et Swallow John by Mice” Credit: Springer Science and Bus Media B V as conveyed through Copyright Clearance Center, Inc. Center, Clearance Copyright through conveyed BVas Media Bus and Science Springer

Number of revolutions per day

Selection ofExercise AbilityinMice Use thetrendsindatatomakeapredictionabout numberof 10 000 12 000 What patternsdoyouseeinthedata? Adapted from “Artificial Selection for Increased Wheel-Running Behavior in House House in Behavior Wheel-Running Increased for Selection “Artificial from Adapted 2 000 4 000 6 000 8 000 0 0 1 In manybirdspecies,malesarebrightly colored,whilefemalesaredullin 2 Generations 3 4

EXPLORATION 3

Principles of Natural Selection

Charles Darwin was not the only person to develop a theory to explain how evolution may take place. An English naturalist named Alfred Russel Wallace independently developed a theory very similar to Darwin’s. Both Darwin and Wallace had studied the huge diversity of plants and animals in the tropics, and both had studied the fossil record. They also were both influenced by the work of Thomas Malthus and his principles of economics. Malthus published a book in 1798 in which he discussed how increasing human populations would challenge the world’s ability to produce enough food for everyone. Both Darwin and Wallace applied Malthus’s ideas to the pressures experienced by plants and animals as populations increased. They noted that no species dominated the world, because some resource limited their ability to reproduce and survive. In an environment where resources are limited, individuals must compete for them. Those organisms that compete successfully go on to reproduce and pass on their characteristics.

EXPLAIN Select the correct terms to complete the statement about resource limitations. Malthus described how resources limit the growth of plant | human | bacteria populations. Darwin and Wallace applied the ideas of Malthus, to state that limited resources could improve | limit the ability of some individuals to pass on their characteristics through adaptation | extinction| reproduction.

In 1858, the ideas of Darwin and Wallace were presented to an important group of scientists in London. In 1859, Darwin published his ideas in the book On the Origin of Species by Means of Natural Selection. The theory of natural selection explains how evolution can occur. Natural selection is a mechanism by which individuals that have inherited beneficial adaptations show differential reproductive success. This theory is built on the premise that more individuals are produced in each generation than can survive in any environment where resources are limited.

Genetic Variation

Darwin’s theory of evolution by natural selection was based on observed FIGURE 10: Variation in coat patterns among plants and animals that he and others studied. What he did color can be seen in jaguars not understand was how these changes occurred. About six years after the and their offspring. publication of On the Origin of Species, a little-known monk named Gregor Mendel published his research on genetics and the basic principles of heredity. Mendel’s work showed that heritable factors, or traits, are passed down from parents to offspring. We now know that traits are coded for by genes, which are portions of a DNA molecule. Different variations of the same gene are called alleles. The jaguar cub shown in Figure 10 inherited a combination of

© Houghton Mifflin Harcourt Publishing Company • Image Credits: ©AP Images alleles that resulted in it having a different fur color than its mother. Therefore, there is variation in coat color in the jaguar population, and some variations may prove more beneficial than others in a given environment. Variation in the alleles between individual organisms within a population is called genetic variation. Genetic variation is the basis for natural selection.

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Genetic variation is increased by a process called meiosis and sexual reproduction. Meiosis is the type of cell division that results in sex cells: eggs in females and sperm in males. Genes are separated during meiosis. If the genes are not linked, they will separate independently. As genes are lined up and shuffled in different ways during meiosis, various combinations of genetic material are made, as shown in Figure 11.

FIGURE 11: Chromosomes separate independently during meiosis. As a result, sex cells have many different combinations of genes. Possibility 1 Possibility 2

two equally probable arrangements of chromosomes at metaphase I

metaphase II

daughter cells

combination 1 combination 2 combination 3 combination 4

In sexual reproduction, the offspring receives two forms of each gene, one from FIGURE 12: Sexual reproduction increases genetic variation. each parent. In this way, sexual reproduction produces an organism with a unique combination of inherited traits. A species that reproduces using sexual reproduction will end up with populations of unique individuals that possess all kinds of traits. For example, Figure 12 shows the variation that can be seen in color patterns in a population of Asian beetles. It is this type of variation that natural selection acts on. Mutations can also increase genetic variation. If a mutation occurs in a sperm or egg cell, it can be passed on to an organism’s offspring and increase genetic diversity within a population. Keep in mind that natural selection acts on physical traits rather than on the genetic material itself. New alleles are not made by natural selection—they occur by genetic mutations. In addition, these mutations must be heritable, or passed down to offspring. Only mutations that occur in sex cells are passed on to offspring.

MODEL Explain how you could have modeled a new trait arising from a mutation in the owl and mouse simulation of natural selection. © Houghton Mifflin Harcourt Publishing Company • Image Credits: ©blickwinkel/Hecker/Alamy

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Overproduction

The work of Thomas Malthus inspired many of Darwin’s ideas about modification by natural selection. In his work, Malthus pointed out the potential of human populations to grow exponentially if there was a constant birth rate and ideal conditions. Such conditions would include unlimited resources and an absence of disease. However, populations do not grow in an unchecked way. As Malthus pointed out, human populations are limited by many factors, such as disease, war, and limited resources.

Human Population Growth

FIGURE 13: Malthus predicted population that population growth would food outpace food production, causing production a “Malthusian catastrophe.”

Malthusian catastrophe Quantity

Time

EXPLAIN Select the correct terms to complete the statement about population growth. Not all words will be used. exponential linear resources competition

Most populations do not experience growth because the in a given environment are often limited, which increases among individuals.

Competition

FIGURE 14: In competition for resources, some Darwin noted that more offspring are born than can individuals will out-compete others. survive and that, without limits, any one species might overrun Earth. However, environments place limits on population growth, where some individuals are more successful at survival than others. Those individuals that survive and produce offspring will have their traits passed on to later generations. © Houghton Mifflin Harcourt Publishing Company • Image Credits: ©RooM/10kPhotography/Getty Images Building on Malthus’s ideas that there are limits to human population growth, Darwin reasoned that a similar struggle for resources took place in nature. The challenge is for each individual to be better at bi_cnlese539273_582a obtaining available resources, such as food, water, 10-31-16 and shelter. Leslie Kell Lesson 3 Theory of Natural Selection 239 CorrectionKey=CA-B DO NOT EDIT--Changes mustbemade through “File info” 240 Unit 4 Evidence forEvolution reproducing altogether. Theyjustreproduced alittleless. other jaguarsinthepopulation. Jaguarsthatatelessdidnotnecessarilyalldieorstop the changeinclimate,jaguars thathadlargerteethandjawsahigherfitnessthan environment. Anindividualwith highfitnessiswelladaptedtoitsenvironment.After produce moreoffspringrelative toothermembersofthepopulationinagiven In biology,thetermfitnessisameasureofability anorganismtosurviveand showed variationsofjawandtoothsizethatbecameimportantforsurvival. to eat,sothejaguarshadeatotheranimals,suchasreptiles.Thejaguarpopulation shortage offoodduetothechangingclimatethattime.Fewermammalswereavailable 11 Natural selectioninjaguars,shownFigure15,isawell-studiedexample.About competition, andadaptation)tosupportyouranswer. over time?Usethefourprinciplesofnaturalselection(geneticvariation,overproduction, environmental conditions. every followinggeneration,aslongthetraitcontinuestobebeneficialinexisting for survivalandreproductionintheirenvironment.Moreindividualswillhavethetrait natural selectionwillresultinaspeciespopulationwithadaptationsthatarewellsuited to livelongerandproducemoreoffspringthatsharethoseadaptations.Overtime, competes againstinitsenvironment.Moresuccessfulindividualsare“naturallyselected” Sometimes, acertainvariationletsanindividualsurvivebetterthanotherindividualsit Adaptation PREDICT FIGURE 15: 000 yearsago,manyspeciesfacedextinction.Largecats,includingjaguars,a a

variation inthepopulation. jaws andteeth(skull1)duetonatural jaguars maybebornwithslightlylarger supported bytheenvironment.Some produce moreoffspringthancanbe Like manyotherspecies,jaguarscan skull 1

skull 1 Why mightlargerjawsandteethbecomemorecommoninjaguarspecies Natural selectionhasled tochangesinthejaguarspeciesovertime. skull 2 skull 2

jaguars thatcaneatonlymammals. survive andtohavemoreoffspringthan reptiles. Thesejaguarsaremorelikelyto to eatarmoredanimals,suchasshelled Jaguars withlargejawsandteethareable

© Houghton Mifflin Harcourt Publishing Company Select allcorrectanswers. common preconceptionsabouthownaturalselectionoccurs. changes intheenvironmentcaninfluencefitness.Italsoisusefultoexaminesomeof To fullyunderstandthetheoryofnaturalselection,itisimportanttoconsiderhow Understanding Natural Selection to findmatesandpassontheirgenes. be carriedbythewindtoanewlocation.Asresult,thesemaleshavemoreopportunities lower bodyweightmakesiteasierforthesemalestocastastrandofsilkintotheairand individual. Forexample,beingsmallisbeneficialforsometypesofmalespiders.Their It isimportanttonotethatfitnessdoesnotsimplymeanbeingthebiggestandstrongest disadvantage in thefuture. for thechanged environment.Withevolution, atraitthatisanadvantage todaymaybea favored productionofsmall, softseedsandsmall-beakedbirdswerenowbetteradapted when thesupplyoflargeseeds decreasedafteranunusuallywetperiod.Theseconditions The numbersoflarge-beaked finchesonthisGalápagosislandkeptrisinguntil1984, 1978 survivors.Ninetybirdsweremeasuredtoconstructthehistogramonright. histogram ontheleft.Afterdrought,Grantsagainmeasuredbeaksizesof In 1976,atotalof751birdsweremeasured.Thedistributionbeaksizeisshowninthe The twographsshowninFigure16representthenumberofbirdswitheachsizebeak. However, therewerestillplentyoflarge,tough-shelledseeds. A droughtin1977reducedtheamountofsmall,softseedsthatfinchespreferred. within apopulationofmediumgroundfinchesonDaphne,onetheGalápagosislands. and RosemaryGrantobservedanexampleofnaturalselectionactingonexistingtraits As anenvironmentchanges,differenttraitswillbecomebeneficial.EcologistsPeter Changing Environments INFER d. c. b. a. conveyed through Copyright Clearance Center, Inc. Center, Clearance Copyright through conveyed as Press University Princeton of permission by reproduced and Adapted Press. University Princeton by Credit: Small-beaked fincheswerebetter abletocracklarge,toughseeds. Large-beaked fincheswerebetterabletocracklarge,tough seeds. The numberoffincheswithlargebeaksincreased. The numberoffincheswithsmallbeaksincreased.

Number of finches What canyouinferabouthowthefinchpopulationchanged afterthedrought? 30 60 90 0 by Peter R. Grant. Copyright © 1998 ©1998 Copyright Grant. R. Peter by Darwin’s of Finches Evolution and Ecology from Adapted 6 1976 AllDaphneBirds Beak depth(mm) 8 10 751 birds 12 Grants’ FinchStudyData 14 12 0 4 8 6 Beak depth(mm)

1978 Survivors 8 10 90 birds 12 14 Lesson 3 Theory of NaturalSelection a drought. size before andafter show finch beak in thesegraphs FIGURE 16: The data 241 DO NOT EDIT--Changes must be made through “File info” CorrectionKey=CA-B

Addressing Preconceptions About Natural Selection It is tempting to assume that any feature on an organism must be the ideal trait for that organism’s environment. However, not all traits are adaptations. For example, most vertebrate animals have red blood. Other animals might have blood that is blue, green, yellow, or even purple in color. However, animals with red blood do not survive better than animals with a different color of blood. Instead, blood color results from its chemical makeup. While the chemistry might be a result of an adaptation, the color itself is not. It also is important to keep in mind that natural selection does not produce individuals who are perfectly suited to their environment. This is partly because organisms have combinations of traits that result from complex sets of tradeoffs. For example, having large horns may help an organism fight successfully for mates, but they may make it difficult for the animal to escape predators as effectively as it could with lighter horns. It would be difficult for selective pressures to produce “ideal” traits, because a trait that is ideal for one function may be less than ideal, or even harmful, in other situations.

APPLY Describe at least two ways in which the large FIGURE 17: Large horns provide some benefits, but also come with costs. horns on the sheep shown in Figure 17 could reduce their fitness.

Another reason natural selection does not produce ideal traits is that natural selection acts only on traits that already exist. Genetic variation within a population is what allows for the environment to “select” for certain traits. New alleles are not made by natural selection—they occur by genetic mutations. Many mutations have harmful results and are therefore not likely to produce a trait that is beneficial in a given environment. However, some mutations lead to traits that might be advantageous to certain individuals. A mutation could change an organism’s DNA in a way that leads to the production of a new type of protein. If this results in a trait that increases an organism’s fitness, this trait would be selected for. Therefore, new traits can occur, but they are not made through natural selection. Another common preconception about natural selection is that individuals can adapt to their environment. Natural selection leads to changes in populations, not in individual organisms. Evolution is a change in the proportion of alleles in a population over many generations. Therefore, individuals do not adapt to their environment over the course of one lifetime. Adaptations occur in populations, and those adaptations evolve over time through the process of natural selection. This process may take millions of years, or it may occur very quickly, as it does in single-celled organisms, such as bacteria. © Houghton Mifflin Harcourt Publishing Company • Image Credits: ©Corbis/W. Perry Conway/ Getty Images

Evidence Notebook Plants that attract hummingbirds often produce nectar that is high in sucrose. This is a key nutrient that supports a hummingbird’s high metabolism. Use the principles of natural selection to explain this trait in certain plants.

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TAKE IT FURTHER

Data Analysis

Antibiotic-Resistant Bacteria

Antibiotics are medicines used N. gonorrhoeae Resistance, United States, 1987-2011 to kill disease-causing bacteria. Studies have shown that certain FIGURE 18: N. gonorrhoeae shows some level of resistance to many species of disease-causing bacteria types of antibiotics. N.N. gonorrhoeae gonorrhoeae Resistance, Resistance, U.S., U.S., 1987–2011 1987–2011 have evolved to be resistant to 3030 various antibiotics. The Centers for TetracyclineTetracycline resistance Disease Control and Prevention resistance 25 (CDC) found that doctors were 25 PenicillinPenicillin resistance prescribing antibiotics when they resistance 20 Fluoroquinolone weren’t necessary. Additionally, 20 Fluoroquinolone resistance patients were not taking their full resistance 15 Reduced antibiotic doses. Both practices 15 Reduced

Percent cefixime have led to bacteria developing Percent cefixime 10 susceptibilitysusceptibility antibiotic resistance. 10

The bacterium Neisseria 55 gonorrhoeae causes gonorrhea. This infection affects organs of 00 the reproductive system, as well 19871987 19921992 19971997 20022002 20072007 20122012 as parts of the urinary tract. If left YearYear untreated, an infected person may Source:Source: The The Gonococcal Gonococcal Isolate Isolate Surveillance Surveillance Project Project (GISP), (GISP), quoted in "Antibiotic Resistance Threats in the United States, 2013" (CDC) lose the ability to produce children. quoted in "Antibiotic Resistance Threats in the United States, 2013" (CDC) These bacteria are transferred from one person to another through fluoroquinolone antibiotics since the bacteria has been resistant to sexual activity. around 2000. This resistance can both penicillin and tetracycline N. gonorrhoeae has now developed be attributed to the increased use since the late 1980s and continues varying levels of resistance to most of this antibiotic during this time to be resistant. antibiotics, including penicillin and period. The graph also shows that tetracycline. The bacteria is also developing resistance to other Evidence Notebook Answer the following questions in your antibiotics. Cefixime is starting to show susceptibility to resistance. Evidence Notebook. It is recommended that cefixime 1. What happened to the bacteria’s penicillin resistance from 1987 to 1990? be used with other antibiotics so 2. Make a model to show the changes in resistant traits in the population of bacteria the bacteria do not become fully over time as they were exposed to antibiotics. resistant to it. 3. Why is it important that a patient complete their entire course of antibiotics, even The N. gonorrhoeae resistance if their symptoms appear to disappear? graph in Figure 18 shows Why do scientists need to continually develop new antibiotics to treat bacterial

bi_cnlese811966_897abi_cnlese811966_897a MODELINGFinal NATURAL NATURAL BIOMECHANICS OF Go online to choose one FinalSELECTION SELECTION TODAY STAG BEETLE JAWS of these other paths. 11-8-1611-8-16 LeslieLeslie Kell Kell

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EVALUATE

Lesson Self-Check

CAN YOU EXPLAIN IT?

FIGURE 19: Hummingbirds have a bill that allows them to feed from nectar-producing flowers.

Hummingbirds have a variety of adaptations, including uniquely-shaped bill and tongue structures that allow them to effectively feed from nectar-producing flowers. The flowers, in turn, have adaptations that make them especially attractive to the hummingbirds. These adaptations include bright coloration, slender shapes matched to the curve of a hummingbird’s bill, and the production of sugar-rich nectar. These flowers are often odorless, which makes them less attractive to bees or other insects that rely on their sense of smell to find food sources. Research indicates that hummingbirds and the flowers they feed from evolved together. As hummingbirds changed over time, so too did the flowers. Evolution isn’t a one-way street. Instead, changes in one species can have a profound effect on an entirely different species, as is the case with hummingbirds and flowering plants.

Evidence Notebook Refer to your notes in your Evidence Notebook to construct an explanation for how adaptations in hummingbird populations influenced adaptations in the flower populations from which they feed, and vice versa.

1. Make a claim about how natural selection influences the traits in the hummingbird © Houghton Mifflin Harcourt Publishing Company • Image Credits: ©Glenn Bartley/All Canada Photos/Alamy and flower population over time. 2. What evidence supports your claim? Consider how the shape of the hummingbird’s bill may have influenced changes in the shape of flowers that it feeds from. 3. Explain how natural selection might affect the hummingbird population if an environmental change affects the flower populations in its habitat.

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Name Date CHECKPOINTS

Check Your Understanding 6. Use the correct terms to complete the statement about natural selection. 1. Which of these traits are most likely to be adaptations for butterfly caterpillars in a butterfly overproduction competition population that lives in a meadow? Select all adaptation genetic variation correct answers. a. bright coloration that makes them highly Natural selection can be modeled by visible representing “beaks” with plastic forks, knives, b. thin skin that easily absorbs pesticides and spoons. Participants use their beaks to c. mouthparts that easily chew grass leaves d. behavior that causes them to stop obtain as many beans as possible from a plate of moving when predators are near beans. In this simulation, the different utensils 2. If the climate were to change in an environment, represent , it is more likely that some individuals within a population will survive if and trying to obtain beans represents a. the individuals stop reproducing. over b. the individuals are genetically limited resources. This is typically the result of identical. , as more c. there is genetic variation within the population. individuals are born than can survive. Having more d. the individuals reproduce asexually. participants take on the form of beak that was 3. Use the correct terms to complete the statement most successful at obtaining food is one way to about natural selection. represent . Natural selection acts on traits | chromosomes in a(n) individual | population. 7. Match each piece of evidence to the way in which it influenced Darwin’s theory of natural selection. 4. Which of the following are key elements of Darwin’s theory of evolution by natural selection? Organisms are Select all correct answers. artificial selection adapted to their a. genetic variation environment. b. genetic engineering Geological forces fossils of extinct c. fitness have changed Earth organisms d. adaptation over time. e. independent assortment Humans can serve as Galápagos tortoises 5. How do mutations lead to genetic variation? the selective agent. a. Mutations directly result in changes in an sea shells above the Species have changed organism’s traits. © Houghton Mifflin Harcourt Publishing Company seashore over time. b. Mutations produce random changes in an organism’s DNA. c. Mutations lead to a random arrangement of chromosomes during meiosis. d. Mutations decrease the variety of traits observed in a population.

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CHECKPOINTS (continued)

8. Explain how longer necks in giraffes might be selected for by natural selection over time. How might this adaptation benefit giraffes?

9. How did the work of farmers and breeders in England influence the work of Charles Darwin? Use examples to support your explanation.

10. What effect did Darwin’s travels to the Galápagos Islands have on the development of his theory of natural selection?

MAKE YOUR OWN STUDY GUIDE

In your Evidence Notebook, design a study guide that supports the main ideas from this lesson: Many scientists made observations and developed ideas about evolution, but it was Charles Darwin who developed the theory of evolution by natural selection. Natural selection is a process in which overproduction, variation, and competition lead to the adaptation of populations over time. Remember to include the following information in your study guide: • Use examples that model main ideas. • Record explanations for the phenomena you investigated. © Houghton Mifflin Harcourt Publishing Company • Use evidence to support your explanations. Your support can include drawings, data, graphs, laboratory conclusions, and other evidence recorded throughout the lesson. Consider how the evidence Darwin and other scientists collected supports the idea that natural selection changes traits in populations over time.

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